The Right Stuff: Inside the Omega Speedmaster Professional - Part 2

May 08, 2007,01:05 AM

The Right Stuff:  Inside the Omega Speedmaster Professional
By: Jack Forster

Part II:  Anatomy of a Legend.




Like many watches that have a rich cultural as well as horological history (the Rolex Submariner springs to mind) it's very hard to actually see the Speedmaster as a watch rather than as a point of entry into the legacy of manned space flight which it represents.



But a watch it is.  Our particular Speedmaster, sold to its original owner in 1999, is the most basic model currently available – with largely the same dial that it had in 1970, when Jack Swigert was staring at the dial of his in the chilly, dark, cramped cockpit of the Lunar Module, waiting to count down the 14 seconds of engine firing that would correct their trajectory so as to keep them in their (very narrow) entry corridor.  The case of the Speedmaster, with the bombe lugs and at 40mm in diameter, was a large watch for its time but nowadays it seems positively gracile.  An eye jaundiced by overmuch consumption of 45mm and larger cases can hardly believe that such a modest looking device was for many years the astronaut's watch of choice (the Russian cosmonauts were fond of them as well) – one just expects something, well, more macho .  However, the Speedmaster was made to a different standard of aesthetics, and even today, the size of the case and the unnecessarily decorative twist to the lugs give the eye an immediately pleasant impression.  In its modest way, the case is even beautiful, sexy – not a bad thing, frankly, in a high stress flight environment; the voice used in modern jet fighters for warning recordings is seductively female (pilots have nicknamed it Bitching Betty – "Pull up, Pull up.  Dear." )


 It may not have the garish flash of many a more recent watch but there is something to be said for its lean, practical, enticing lines.  Why Miss Jones, without your glasses. . . .


Speaking of pretty faces, let's talk about the dial.  The balance and proportions of each element are so close to perfect as to run the risk of essentially being invisible as such.  The tri-compax arrangement of the subdials is perfectly offset by the Omega logo, and, in three different descending fonts, the words Omega Speedmaster Professional , forming a triangle whose lines, when extended, exactly intersect the center of the two lateral subdials.  The diameter of the subdials themselves is perfectly inscribed within an imaginary circle formed by the inner edges of the luminous hour indexes; the stick hands are perfectly legible, wide enough to be easily visible but not so massive as to obscure the view of the subdials, and the chronograph seconds hand has a distinguishing arrowhead shaped element, beginning about halfway along its length, which sits, when the chronograph is zeroed, neatly, perfectly, within the Greek letter Omega at the top of the dial.  The base of the arrowhead perfectly lines up with the outer edge of the circular base of each of the chronograph hands as well, which can be observed by stopping the chronograph at 15 seconds.  The charcoal matte black dial sets off the glossy metallic black of the tachymeter ring, and the slightly domed, Hesalite (acrylic) crystal gives the entire watch an approachable tactility – one or two Martinis (vodka, shaken, not stirred!) and Miss Jones just might let her hair down a little.


It's worth noticing that these nearly perfect proportions are the result of the size of the movement and the size of the case being in harmony – the tendency for modern watches to get so big they look like something from the Acme factory rather than a watch manufacturer has resulted in the notorious "cross-eyed chronograph" syndrome, where the subdials are crowded together disproportionately close to the center of the dial, making the watch as a whole look slightly ridiculous – the horological equivalent of Spinal Tap stuffing socks down their trousers.  Such self-parody is beneath the Speedmaster.  One is reminded of James Bond's comment about an American sports car compared to his beloved 1954 Bentley R-Type:  That sort of hot rod job's alright for kids who can't afford a real car. 


The Works:  Caliber 1861


As we've already noted, in 1968, the original cal. 321 was replaced with caliber 861, seen here in all its rose gold glory:



In 1996, the rhodium plated caliber 1861 replaced caliber 861.  Unscrewing the caseback (proudly emblazoned with the words "Flight Qualified by NASA for All Manned Space Missions" and "The First Watch Worn on the Moon") reveals a grey antimagnetic dust cover and a solid metal spacer ring – not especially thick, as the Speedmaster and its movement are a good fit.




Aside from the obvious change in finish, note that an additional jewel has raised the count to 18 and that, just above the central chronograph wheel, a plastic brake has replaced the metal brake found in caliber 861.  The display back version of the Moonwatch has retained the metal brake and sports a more elaborate finish in general; however mechanically it is otherwise identical to its less decorated sibling.


The first impression one has on examining cal. 1861 is of an overbuilt, solidly constructed piece of equipment designed to pragmatically and practically fulfill the job of timing intervals of elapsed time.  There is nothing that strikes one as a superfluous complexity; there are no awkwardly arranged bits that speak to a module added to what started life as a time only movement; no bridge for a nonexistent rotor; and the general thickness and solidity of every part – plates, bridges, wheels and springs – makes one feel assured that here's a piece of machinery designed and refined from the ground up to get the job done . 


The Power Train


In disassembling the watch, the first order of business is to remove the chronograph bridge and chronograph mechanism; stripping off the top layer of machinery on the plate leaves us with the power train exposed.  Since our main point of interest is working our way through how this type of chronograph works, we'll start by looking first at the power train and then moving on to the chronograph mechanism itself.



With the chronograph mechanism removed, we can see that the construction of caliber 1861 is actually a ¾ plate layout!  The exposed top plate allows us to observe the large balance, smaller cock for the escape wheel at the 8 o'clock position, and the jewels for the escape, third, and fourth wheels.  Notice also that the train is a 15-jewel train – the two additional jewels in the chronograph bridge raise the count to 17, and in cal. 1861 an additional jewel for the pivot of the chronograph coupling wheel makes it 18 jewels in all. The orientation of the movement is exactly like that of a one hundred and fifty year old pocket watch: the winding crown, if we stop and imagine it in the 12:00 position, puts the fourth wheel arbor at the 6:00 position, right where the seconds subdial would be on a pocket watch – and indeed, in the Speedmaster Professional, the seconds hand runs in a subdial opposite the crown, attached directly to the extended arbor of the fourth wheel.  A machine applied striping and smoothly finished edges devoid of beveling or any other unnecessary adornment completes the picture.  Removing the ¾ plate (well, all right, the train bridge):


exposes the train itself.  Again, no surprises here – just good, solid work; with the usual arrangement – mainspring barrel geared to the large center wheel (remember, during running, the mainspring barrel itself is rotating, whereas in winding the barrel is stationary and the barrel arbor rotates to wind the mainspring, turned by the crown wheel) which then turns the third, fourth, and escape wheels.  The extended pivot for the gear that will drive the central seconds counter for the chronograph – the so called "driving wheel," can be seen on the fourth wheel.  Come to think of it, gussy this movement up with some Geneva stripes and beveled edges, and maybe move the crown and you'd have a pretty darned nice ¾ plate "Saxon" style movement.  Good size for a modern, slightly big hand-wound watch. . . . no, no, perish the thought!


The Balance and Escapement


The lever escapement and 15 tooth escape wheel interact with a large diameter balance, vibrating at 21,600 vph, and in general exhibit the same pragmatic, efficient finish as the rest of the train:


(This balance is actually from a Cal. 861; note the blued hairspring.)

The hairspring is a flat Nivarox hairspring (changed over from the Breguetovercoil in cal. 321 in 1968) and the balance is very typical of watches of this era – kept somewhat light, to reduce the risk of damage to the balance pivots when the watch experiences a shock, but not so light as to undesirably reduce the moment of inertia.  Like all mechanical solutions a compromise but a good one –the basic idea is to – well, strike a balance.  (Seiko automatic chronographs, such as calibers 6139 and 6138, which were designed and sold starting in 1969, have very similar balances.)  The eccentric fine regulator and nicely done curb pins on the regulator sweep complete the picture of a balance and escapement designed to hold a stable rate and once adjusted and regulated, resist shock.


Well, that's the heart of the watch – but this is after all a chronograph.  At this stage a useful thing to bear in mind is that servicing and adjusting a chronograph carries some interesting challenges along with it.  The basic problem with any watch is that you want the rate to be as stable as possible, and in order to achieve that goal, the balance amplitude has to stay in the neighborhood of a 'sweet spot' generally agreed to be around 280-290 degrees at full wind in the horizontal positions, which minimizes positional error.  Anything getting down to around 180 degrees or less, or conversely 300 degrees or above, is going to amplify positional deviation due to poising errors in the vertical positions.  Now the problem with a chronograph is that you have different loads on the train depending on whether the chronograph is switched on or off (one of the selling points of a vertical clutch chronograph, in fact, is that the chronograph wheel is always engaged –it's either turning the seconds totalizer hand or not depending on whether the clutch is engaged or not, but the load's not dramatically different with the chronograph on or off.)  An acceptable drop in amplitude is generally thought to be somewhere in the neighborhood of 20 to 30 degrees when the chronograph is switched on, and we can immediately see that with an amplitude of 280 degrees, in a properly adjusted chronograph, switching on the chronograph if the watch is fully wound gets us nowhere near the problem zone.  As the watch runs down, of course, amplitude starts to drop- after 24 hours, it's probably somewhere in the ballpark of 200 degrees or so, in the vertical positions – but if you're winding your watch once a day, the chances of running the chronograph for a long enough period of time to notice significant inaccuracy in elapsed time situations are probably nonexistent.


The caveat here is that the chronograph has to be adjusted properly and presumably, serviced regularly, otherwise the degradation of lubricants is eventually going to compromise amplitude enough for inaccuracies over extended elapsed time periods to be noticeable.  With that in mind, let's have a look at the chronograph mechanism itself.


Following the sequence of events in the operation of a chronograph is one of the things that make horology, as a hobby, fun .  You have to be able to hold several different operations in mind at once since several different things are happening at once.  But we can do this.  In the immortal words of Apollo Flight Director Gene Krantz (Mr. Failure Is Not An Option), let's work the problem, people. 


Basic Concepts In Chronograph Operation


All right now. . . if a picture is worth a thousand words, a moving picture is worth. . . well, more:



OK, let's get ourselves oriented here.  We are now looking at what happens during starting, stopping, and reset of the chronograph, if we look at the movement from the back, and upside down relative to how it's usually worn.  Notice that the start button in our pictures and in the animation is in the lower position, whereas when the watch is worn, it's in the upper (2:00) position.


Let's get the basic principles in place.  We've already seen that under all the confusing looking bits and pieces of the chronograph train, there's a basic, bog-standard gear train leading from a mainspring barrel to an escapement.  The trick, in a chronograph, is that power from the train has to somehow be coupled, via some sort of clutch mechanism, from the power train to the chronograph train when the start/stop button is pushed.  Then, when the chronograph is stopped, the power train and chronograph train have to be disengaged from each other.  Finally, once the elapsed time is read, the reset button has to be pushed, which resets the chronograph hands to zero, ready to time another – well, horse race, parking meter, or LM descent engine burn, as the case may be.


We'll get into the specifics shortly, but for now, notice basically what happens as the chronograph is started and stopped.  Pushing in the start/stop button causes a series of levers to move which make the component at the 12:00 position move back and forth – this part, which consists of two cams , one on top of the other, performs the same function as a column wheel does in a more traditionally constructed chronograph.  The two cams are made to rotate back and forth through the action of a connecting lever actuated by the start/stop button.  As the lobes of the cams rotate, they cause other levers to move, which engage and disengage the chronograph train from the power train.


Finally, observe what happens during reset to zero.  Instead of the start/stop pusher being depressed, the reset pusher is depressed.  This causes a complex looking lever – the reset hammer – to fall, and the flat striking surfaces of the reset hammers land on the heart pieces of the seconds, minutes, and hour totalizers, causing them to very rapidly rotate into the zero position.  The chronograph is now reset and ready to go.


With the basic principles in mind, let's look in detail at each phase of the chronograph's operation.


Starting the Chronograph


Let's take a close look at the sequence of events in starting the chronograph.


When the pusher is depressed, it causes a long L-shaped lever – the operating lever – to move inwards.  The tip of the operating lever has a notch cut in it that receives the point of a small part called the shuttle .  The point of contact between the operating lever and the shuttle is hard to see in the animation since it's partially hidden by the reset hammer and the operating lever yoke , which is attached to a strong spring shaped like a backwards letter C that forces it to return to its starting position when pressure is released on the chronograph start/stop pusher.


If we remove the reset hammer, we can clearly see the nose of the six-sided shuttle in its notch on the operating lever, with the operating lever yoke engaged with a pin on the upper surface of the shuttle:



Notice that when the start/stop pusher is depressed, the operating lever moves to the left, pushing the shuttle into the lower cam.  This causes both the upper and lower cams to rotate, causing the chronograph to start.  The return force of the operating lever yoke's spring then pushes the shuttle, and hence the operating lever back into their "resting" position when pressure's taken off the start/stop pusher (the spring inside the pusher itself causes it to return after being depressed).


Hey, I said we could do it, I didn't say it would be easy.  Hang in there!  Here's a picture of the shuttle with the reset hammer, the operating lever and the operating lever yoke removed:



Funny looking little gizmo, ain't it?  But that's what's coordinating the entire operation of the chronograph- that and the cams on the left that it causes to move.  This is what I meant before when I said that a lot of mechanical solutions were non-obvious or counter-intuitive; this is not the kind of thing that would immediately occur to most of us if we set ourselves to the task of figuring out how to make a chronograph!  If you're wondering who came up with this system for what is now generally known as a shuttle and cam chronograph, the first patent for a non-column wheel, cam-actuated chronograph (sometimes also referred to as a heart piece limiter chronograph) was by the firm of Landeron, in 1940.  The original Landeron patent was for a three-button design, and later designs –including calibers from Venus, Valjoux, and Lemania – employed cam systems, simplified and made more robust than the original Landeron patent.  A modern shuttle and cam caliber like the Omega 1861 is the end result of over a hundred years of chronograph design and nearly sixty years of tweaking the design of cam actuated chronographs, and it is reliable and robust, as well as being less expensive to manufacture than a column wheel chronograph caliber.


Anyway, back to starting our chronograph – we've gotten as far as seeing how the start button gets the shuttle to play nice with the cams; let's see what happens next.


First order of business is we have to get power from the fourth wheel – the point of connection between the chronograph train and the power train – to the chronograph train.  Let's look at our animation again.  If you watch the upper cam closely, you can see it rotate clockwise when the chronograph is started.  In rotating clockwise, the lobe on the left lifts the arm of a long lever visible on the upper left side of the animation known as the hour recorder yoke.  The hour recorder yoke actually has to do, as the name implies, with the hour recorder, and we're not there yet.


Now, turn your attention to the lower cam.  During starting, the lower cam rotates clockwise as well.  Look closely and you'll be able to see the shuttle pressing against it from the opposite side.  If you observe carefully, you'll be able to see, during starting, a lobe of the lower cam rotating clockwise, moving out of the way of the nose of a lever (underneath and roughly parallel to the hour recorder yoke), unblocking it  – this lever is more properly known as the coupling yoke , and it carries on it the coupling wheel.


In the animation, there are three wheels visible on the left and center of the movement.  The bronze colored one on the farthest left is mounted on the pivot of the fourth wheel – the watch in the animation isn't actually running but in real life, this wheel, the driving wheel , is constantly turning as the fourth wheel turns once per minute.  When the lower cam moves, unblocking the coupling yoke, a small spring (just visible to the far left, under the hour recorder yoke) pushes the coupling yoke to the right .  The (silver colored) coupling wheel mounted under the small bridge attached to it goes along for the ride, dropping into position between the driving wheel and the centrally located, brass colored chronograph wheel .  At this point – Joy of Joys! – We have connected the power train to the chronograph train, and the central seconds register hand, which is attached to the pivot of the chronograph wheel on the dial side of the movement, at long last starts to turn, ticking down our 14-second burn. . .


Left, the brass colored chronograph driving wheel; middle, the coupling wheel (with its upper pivot in the 18 jewel), and to the right, the chronograph wheel.


In the above picture, you can see two funny looking screws that look like someone shaved off their flanks parallel to the slots.  Both are eccentric screws; the one on the lower left adjusts the depth of engagement of the coupling wheel teeth with the driving wheel, and the one in the center right, just between the cams and coupling wheel, can be rotated to control the depth to which the coupling wheel teeth engage the chronograph wheel.  Both are critical points of adjustment.  If the depth is too shallow, the chronograph wheel won't engage securely with the driving or coupling wheels, and if it's too deep, the gears will actually lock up and not turn at all.  Omega recommends that the depth of engagement be equal to two thirds the depth of the teeth of the coupling wheel with the driving wheel and one third the depth of the teeth of the couple wheel with the chronograph wheel, just in case you think you're the only one who has to deal with pain-in-the-neck details at work.


The eccentric for adjusting the coupling wheel depth with the driving wheel.


Now, we said we finally got power to the chronograph, and we did, but the chronograph seconds hand is not going to start turning unless we do something else at the same time .  The problem here is that each one of the wheels that turn the chronograph hands – including the chronograph wheel itself, of course – is held in place, when the chronograph has been reset to zero (which is where we're starting from) by the reset hammers.  The reset hammers have to be lifted off the heart pieces mounted on the pivots of the wheels for the seconds, minutes, and hour totalizers or the hands won't turn.


Now the reset hammers are designed to more or less instantly snap the chronograph hands back to zero when the chronograph is reset.  How this is accomplished is a rather neat trick.  Let's look at the chronograph wheel.  Mounted on it is a so-called heart piece:


Heart piece on the upper side of the chronograph wheel.


The reset hammer, which is the multi-armed doohickey on the upper right of the animation, has two flat striking surfaces, which, when the hammer falls, drop onto the heart piece.  The heart piece is designed (it is a modification of a geometric figure known as a cardioid ) so that no matter where the hammer falls, it will cause the heart piece to rotate until the flat of the hammer rests against the "top" of the heart – a position that corresponds to the zero position for the chronograph seconds hand.  And so it is for the hour and minute recording runner hands as well.


That means that to start the chronograph, we have to lift the reset hammers out of the way.  Looking again at our animation, we can see that the reset hammer on the movement side has two striking surfaces; one resets the seconds register, and the other the minutes register.  Both need to be lifted out of the way for the chronograph to start running   Lifting the reset hammer is the job of the upper cam (remember that its other job is to lift the hour recorder yoke, which we haven't talked about yet.)  As the upper cam rotates clockwise, the lobe on the right side of the upper cam moves downward and presses on the nose of the reset hammer, lifting it out of the way and allowing the chronograph to run. Simultaneously, the lower cam lifts the white, Delrin blocking lever, which was previously held away from the chronograph wheel by a finger on the reset hammer, but more about that in a bit. 


So here's the story so far during start-up:


    Upper cam: operates the hour recorder yoke (starting the hour register) and simultaneously lifts the reset hammer off the heart pieces of the seconds and minutes registers (we'll look at the hour register reset hammer shortly)
  • Lower cam: receives the shuttle to rotate both the lower and upper cams; also operates the coupling yoke that gets the power flow from the fourth wheel through the driving wheel, via the coupling wheel, to the chronograph wheel while also lifting the blocking lever.


Remember, a key difference between a shuttle and cam chronograph and a column wheel chronograph is that a column wheel rotates continuously in one direction, whereas the cams alternately rotate clockwise and counterclockwise during start, stop, and reset.  The lower cam is held in whichever position it's in by a jumper spring, seen here resting in one of the two notches designed to receive it in the lower cam:


Now that we've gotten the chronograph train engaged, and we've gone as far as getting the chronograph wheel turning, let's take a look at the minutes register next.


If we remove the bridge that covers the chronograph wheel, we can see that the chronograph wheel drives the wheel on which the minute register hand is mounted (the minute recording runner ) via an intermediate wheel (the runner intermediate wheel .) 


To the left is the chronograph wheel, sandwiched between the heart cam on top, and below, a metal disk that carries a finger that engages with the intermediate wheel once per minute.  The chronograph wheel advances with every unlocking of the escapement (in a 21,600 vph movement, that means 6 times per second) but the minute recording runner doesn't run continuously – instead, it jumps forward by one minute increments as the finger on the underside of the chronograph wheel advances the intermediate wheel.


To keep the minute recording runner from simply rotating freely when the reset hammer is lifted off its heart piece, a small jumper and jumper spring, which are affixed to the underside of the chronograph bridge, engage with the teeth of the minute recording runner.  Remember, we removed the bridge to get a look at the minute recording runner and its intermediate wheel, so let's take a quick glance at the underside of the chronograph bridge:


Here we can see the minute jumper and its spring.  The tension exerted by this spring is yet another ticklish point of adjustment.  If the tension on the spring is too great, it will require excessive force transmitted through the chronograph wheel and the intermediate wheel to defeat the spring tension and advance the minute recording runner one tooth.  Too little tension and the minute recording runner may bump forwards or backwards if the watch gets a jolt during running.  Omega recommends that there be a flexure in the middle of the spring of approximately 0.10 to 0.15 mm with the jumper removed. 


One final point, before we turn our attention to the hour register, is to note that the pivot for the chronograph wheel, to which the seconds register hand is attached, runs through the hollow pivot of the center wheel, which we can see if we examine the train again:


To prevent the chronograph wheel from jumping erratically a small tension spring, attached to the train bridge, presses up against the underside of the metal disk on the bottom of the chronograph wheel to secure it in position.  The friction spring is visible in the picture of the movement without the chronograph train and can be seen here in close-up:


This friction spring more than any other single component is responsible for the drop in amplitude a conventional chronograph experiences when the chronograph is started.  A dry surface lubricant is applied to the fork of the tension spring in some iterations of this movement in order to limit the degree to which friction saps additional power from the train.


In a stepwise fashion, we've seen how depressing the start/stop pusher moves the operating lever and shuttle, causing the cams to rotate.  This in turn allows the coupling wheel to drop into place, feeding power to the chronograph wheel and minute recording runner.  (And of course, the cams also lift the reset hammer off the heart pieces for the chronograph wheel and minute recording runner in addition to lifting the blocking lever so they're free to turn.)


At this point an alert reading is probably scratching his or her head and wondering, how does power get to the hour recorder?  And for that matter, where's the hour recorder at all?


Well, the answer is a little unexpected – you will look in vain for the hour recorder on the top plate side of the movement (the side we've been looking at) because guess what – it ain't there.  Unlike the chronograph wheel and minute recording runner, the hour recorder doesn't run off power coming from the fourth wheel – in fact, it's not linked mechanically to the other two at all.  The hour recorder, surprise surprise, runs directly off the mainspring barrel, which means that to see how it engages, we're going to have to flip the whole blessed movement over and look at the dial side.


Bet you didn't see that coming. 


OK, here is the dial side of the movement.


We can see in this picture what is under the dial of the watch – imagine that we've decased the movement, removed the hands, removed the dial, and now we can see the motion works that drive the hour and minute hands, the keyless works for hand setting and hand winding, the stem, and, most importantly, we can see a bridge covering the mainspring barrel, which is at more or less the entire four to six o'clock position (if we think of the stem as being at three o'clock.)  The bit that we want to get turning – the hour recorder runner – can just barely be seen as its edge protrudes out from under the inner edge of the barrel bridge, along with its bushing at six o'clock.


Fortunately for us, we have an animation of the action on the dial side as well:



As with our examination of the top plate action, a few minutes spent getting oriented here will save us a lot of confusion.


Now we have already established that the hour recorder yoke – which, remember, is on the other side of the movement – is lifted up by a lobe of the upper cam during starting.  A projection on the underside of the hour recorder yoke passes through the movement from the top plate side to the dial side, and can be seen as a small pin located at nine o'clock in the dial side animation – you can see it moving slightly to the right during startup of the chronograph.  As it moves, it presses against the switch located next to it, which in turn lifts the hour recorder brake – officially known as the hour recorder stop lever – off the edge of the hour recorder, allowing it to start turning.



Here we can clearly see the pin on the underside of the hour recorder yoke, passing through a hole in the movement and pressing against the switch.


Now, the sixty five thousand dollar question is, where's the clutch that connects the hour recorder to the mainspring barrel?  The somewhat surprising answer is that there isn't any – at least, nothing like the mechanical clutch that engages the driving wheel with the coupling wheel on the other side of the movement.  Instead, a friction fit wheel fitted to the mainspring barrel is constantly engaged with the hour recorder, and it is simply the pressure of the hour recorder stop lever that holds the hour recorder in place and prevents it from turning, even though it "wants to."  To get a better idea of how this works let's take off the barrel bridge for an unobstructed view of the barrel and the hour recorder:



In this picture the barrel bridge has been removed, along with the hour recorder stop lever (much less confusing to call it the hour recorder brake but who am I to argue with Omega) and we can see exposed the silver colored hour recorder runner, as well as, gearing to it, a brass colored wheel, the driving pinion.  The driving pinion is mounted on the mainspring barrel arbor and is held in place against the barrel by the rounded square shaped spring underneath with the clover leaf cutout, which is known as the friction spring for driving pinion.  (Pure poetry, these part names.  They sound so much better in German –Friktionsfeder des Mitnehmertriebes, anybody?) 

(It should be noted that these two pictures show the barrel from a Cal. 861, note the blued friction coupling for the driving pinion.)

Here, with the barrel removed, we can see the driving pinion in place, with the friction spring underneath, and with the barrel disassembled:

We can see the barrel, barrel cover, arbor, the driving wheel, the friction spring, and the two screws that hold the friction spring in place.  The two tongues of the friction spring press down on the top of the dark purplish flange under the driving wheel (beryllium bronze colored in the Cal. 1861), holding it down on the cover plate of the barrel.


Thanks to the downward pressure of the friction spring, if the driving wheel is free to move it will rotate as the barrel rotates, thereby driving the hour recorder –however, the hour recorder stop lever is pressing against the teeth of the hour recorder before the chronograph is started, preventing the driving wheel from turning.  As strange as this arrangement might seem at first, it is the general standard design for driving chronograph hour recorders, and in this seven year old watch, the points of contact between the barrel, driving wheel, and friction spring showed no visible wear.  Not that there's any particular reason why they would – remember, the mainspring barrel only turns when the watch is running (it's the arbor that turns during hand-winding; the barrel's stationary) and the entire barrel turns maybe four times a day.  This is not a high-speed area. 


Notice also, by the way, that before starting the chronograph, the chronograph wheel and minute recorder are held in place by the reset hammer; however, the hour recorder is held in place by the hour recorder stop lever, and the reset hammer for the hour recorder comes into action only during actual reset.


So at long last, the final piece of the puzzle falls into place, and we can see how starting the chronograph works:


    Chronograph wheel and minute recording runner:  reset hammer is lifted to free them to turn; coupling wheel falls into place, allowing power to flow from the driving wheel to the chronograph wheel; chronograph wheel via a finger on its underside drives an intermediate wheel that turns the minute recording runner one increment per minute.
  • Hour recording runner: hour recorder yoke lifts the hour recorder stop lever off the teeth of the hour recorder, freeing it to turn thanks to the power flowing to it from the mainspring barrel via the driving wheel.  (remember: the barrel is turning, not the arbor, so it's actually the friction of the friction spring against the flange of the driving wheel that transfers power from the barrel to the driving wheel.)


And now, at last, she's off.  Swigert at this point very likely had his eyes glued to the dial, and thank goodness, with total unconcern for the drama of the moment and the almost astronomically unlikely sequence of events that produced it, the Speedmaster was doing its job.  The three men, crowded in this narrow space:

with the Rocketdyne built descent engine roaring, executed the maneuver as best they could, despite their misgivings.


"When the ground read out the procedure to us, I just couldn't believe it. I thought I'd never have to use something as way-out as this. And here I was on Apollo 13, using this very same procedure. Because it was a manual burn, we had a three-man operation. Jack would take care of the time. He'd tell us when to light off the engine and when to stop it. Fred handled the pitch maneuver and I handled the roll maneuver and pushed the buttons to start and stop the engine."  – James Lovell.


. . . 11, 12, 13, 14, shutdown!


And we're ready for. . .




Stopping the Chronograph


Having just devoted ourselves to diligent study of both the basic chronograph components, and their coordinated operation in starting the chronograph wheel, minute, and hour recording runners, we are now in a position to easily understand the coordinated operation of the functions of stopping and resetting the chronograph.


Returning to the movement side, and contemplating our movement side animation, the action of the chronograph in stopping is clear.


First, let's direct our attention to the shuttle and lower cam.  Notice that because the lower cam has rotated clockwise during starting, its relationship to the shuttle has changed.  As the start/stop pusher is depressed, and as the operating lever presses home the shuttle, the shuttle now rides against the upper, rather than the lower lobe of the lower cam.  This causes the lower cam to rotate back into the position it was in previously (counterclockwise).  The immediate effect is that the power flow to the chronograph wheel and minute recorder is interrupted.  The coupling wheel travels, on the coupling yoke, out of engagement with the chronograph wheel, which stops turning, and of course no longer causes the minute recorder to turn.


We can also see that the upper cam allows the hour recorder yoke to drop back into its starting position.  On the dial side, this has the effect of releasing pressure on the switch, which in turn releases pressure on the tail of the hour recorder stop lever.  The spring for the hour recorder stop lever (that's the resort de sabot de bloqueurducompteurd'heures to you, pal) then pushes the hour recorder stop lever back into engagement with the hour recorder, which ceases to turn.


Now a critical point to notice on the dial side, is that the chronograph wheel is not held stationary by the reset hammers when the chronograph is stopped during running.  If the reset hammers (which were lifted off the heart pieces to start the chronograph) were allowed to fall into place when the chronograph stopped during running, of course the registers would immediately reset to zero and you wouldn't be able to read the elapsed time. 


The problem here is that the reset hammers are lifted out of the way by a lobe on the upper cam (as we already noted) but, when the chronograph is stopped, the upper cam rotates back into its starting position – this should allow the reset hammer to fall.  But it can't.  The reason is because as the reset hammer is lifted out of the way during starting, a notch on the underside of the reset hammer passes over and then locks on a bolt extending from the reset button.  When the chronograph is stopped, but not yet reset, even though the lobe on the upper cam no longer holds the reset hammer in place, it's still kept from falling back on the heart pieces by the reset bolt.


In this picture, we see the pusher for reset on the right, and the bolt that engages with the notch on the reset hammer.  Notice that the reset hammer is not actually touching the bolt in this picture – that's because the picture shows the watch during running of the chronograph , and in that state, the reset hammer is held away from the heart pieces by the lobe on the upper cam.  However, if we were to push the start/stop button, stopping the chronograph, the upper cam would allow the reset hammer (under the pressure of the reset hammer spring) to start to drop towards the heart pieces – but the bolt would stop it.


There is another critical difference between the stopped and reset state, and the stopped while running state – that is that the chronograph wheel, which must be held in a fixed position while the elapsed time is read off, is held in place by the one plastic component in the watch:  the blocking lever , also often referred to as the chronograph brake.

In this picture, the chronograph is running.  Note that the reset hammer is lifted, and the cam has rotated counterclockwise allowing the coupling wheel to engage the chronograph wheel.  In the upper center of the picture the shuttle is being held in place, away from the lower cam, by the operating lever yoke and its spring (not visible).  Now if you examine the animation again, you will notice something important, which is that in the stopped and reset state, with the hammer dropped into position, the projection on the arm of the reset hammer for the chronograph holds the plastic stop lever off the chronograph wheel.  Equally importantly, when the chronograph is stopped during running, the reset hammer does not fall back into place; this allows the plastic stop lever, as the lower cam rotates clockwise, to fall into place (pushed by its spring) and hold the chronograph wheel in the "elapsed time" position.  Re-starting the chronograph causes the lower cam to rotate counterclockwise again, lifting the stop lever off the chronograph wheel and allowing it to run.


In essence, the chronograph mechanism is a kind of simple, but quite clever computer.  There are two possible inputs: depressing the start/stop pusher (A input) and depressing the restart button (B input.)  Call the initial state (chronograph stopped, hands reset to zero) state a. 


If state a , and input A, then state b  (chronograph starts.)


If state a, and input B, then state a (no change – you can't start the chronograph with the reset button.)


If state b, and input A, then state c  – and this is the clever part; you would expect a return to the ground state, but instead a third state is achieved, the "stopped during running" state.  As we have seen, this state is different from the stopped and reset state – the reset hammers are clear of the heart pieces (on the dial side) instead of pressing on them, and the reset hammers are also locked in place so that only input B (pressing the reset button) when in state c will allow them to fall .  In addition, the plastic chronograph stop lever is free to fall into position and stop the chronograph wheel in state c but not in state a. 


Thus, through the use of only two inputs, the chronograph is capable of remembering it's previous state, and calculating what the next state should be based on adding together the current state, and input.  Understanding the nature of this problem gives us a much better appreciation for the great ingenuity required to solve it.


Reset To Zero


The reset to zero action, on the dial side, is now easy to understand, if we remember the state of the chronograph during the "stopped during running" state.  Pressing the reset button causes the bolt holding the reset hammers above the heart pieces to unlock the reset hammers.  The reset hammers fall, striking the heart pieces on the chronograph wheel and the minute recorder, and both more or less instantly return to zero.


Notice that in falling, a flange on the reset hammer also lifts the plastic chronograph stop lever off the chronograph wheel.  This is essential in order for the chronograph wheel to be able to turn and rotate back to its start position.  The minute recorder, held in place only by the spring jumper, also rotates back into the start position.


On the dial side, reset of the hour recorder is relatively straightforward.  Depressing the reset button, in addition to operating the bolt that frees the reset hammer for the chronograph wheel and minute recording runner, also presses the tail of the hour hammer directly, causing it to pivot and fall into position on the heart piece of the hour recorder runner.  Notice, in the dial side animation, that as it falls home onto the hour recorder runner heart piece, the reset hammer also lifts the hour recorder stop lever free of the hour recorder runner, allowing it to rotate into the start position.  As its spring lifts the hour hammer back off the hour recorder runner, the hour recorder stop lever drops into place to prevent the hour recorder runner from advancing.


The entire chronograph has now been reset, and is ready to time another elapsed event.


We should also note that the reset-to-zero pusher cannot physically be depressed while the chronograph is running.  (It can be depressed after reset to zero but there is no effect.  And of course pushing it when the chronograph is in the stopped-while-running state causes the chronograph to reset to zero.)  The reason is because while the chronograph is running, the tip of the hour recorder stop lever (on the dial side) rests against a small vertical projection on the hour recorder runner's reset hammer:

Pressure on the reset pusher, remember, forces the hour hammer to fall, but during the running state, the hour recorder stop lever is lifted free of the hour recorder runner and blocks the reset hammer from falling – and therefore the reset pusher from being pushed in.


Owners sometimes wonder if it's possible to damage the watch by pressing the reset button while the chronograph is running – theoretically of course, enough pressure will either shear off the protrusion on the reset hammer or perhaps bend the hour recorder stop lever (and dropping the watch so that the reset pusher hits a hard surface during running may indeed inflict significant damage) but as a considerable amount of force would have to be deliberately exerted in order to defeat the blocking of the hour hammer, it's to be hoped that common sense would warn the experimenting owner that such an application of significant pressure is probably inadvisable.


In the Eye of the Beholder


If form following function is beautiful, then the movement of the Speedmaster is a thing of beauty.  In terms of finish, there is very little if anything that could be said to be decorative; most of the embellishments associated with haute horlogerie are resolutely absent.  However, it's also true that there are few, if any, signs of inattention or lapses in solid functional finish, and in this six year old watch, the condition of the movement when opened reflects its robustness – there were virtually no signs of wear of any significance at all in the movement, and the only part replaced (which is routine) was the mainspring.


As a mechanism, as a piece of engineering, caliber 1861 represents the culmination of many decades of chronograph evolution.  There is virtually nothing left to chance in its operation, design, and execution, and in both the reliability of its action and the burly, utilitarian dimensions of its components, the Speedmaster is a watch clearly designed and intended throughout not to dazzle the eye, but rather to do its job and to do it as well as possible.  Even the sometimes derided plastic stop lever for the chronograph wheel is a concession to pragmatism; the plastic's surface properties give it a secure purchase on the small and relatively delicate teeth of the chronograph wheel without any risk whatsoever of damaging them.  The Speedmaster has enjoyed a hard earned reputation for toughness for many decades, and that reputation is clearly well deserved.


  Part III:  Sic Transit Gloria


The Speedmaster, of course, amply repaid the trust put in it by NASA, and performed flawlessly for the crew of Apollo XIII – they ended up splashing down a mere four miles from their target site, which was not only fantastic accuracy considering the circumstances, but also the most accurate splashdown of any manned space mission to date.  The Speedmaster was worn on all subsequent Apollo missions, and was, in fact, recertified for cockpit and EVA operations again in 1972. 


Post mission debriefing, Houston, 1970.  Fred Haise, right, still wears his Speedmaster.


There was political pressure from the Bulova Watch Company at the time to dump the Speedmaster in favor of an American made watch, and Bulova had successfully lobbied the White House to force NASA to adhere to regulations compelling the agency, when possible, to purchase from American suppliers.  A total of sixteen watch companies were notified by NASA that they were planning on establishing a list of qualified products for future astronaut watches.  Bulova did its level best, submitting specially prepared chronographs for a repetition of the Torture Tests, but when the retesting process was completed in December of 1972, the Bulova chronographs had failed.  Dale Myers, Associate Administrator for Manned Space Flight, gave the final word on the subject:


"The special Bulova chronographs purchased by MSC for possible application for Apollo 17 and Skylab, have failed their qualification tests both in humidity and acceleration. I have instructed the Manned Spacecraft Center to take no further action with respect to chronograph testing or other companies' watches. I consider the Bulova watch issue closed."


Well. . . in politics, no issue is ever closed.  In 1978, Bulova was at it again , this time enlisting Senator Jacob Javits of New York, who persuaded NASA to once again open a competition for an official astronaut's watch.  (By this time, incidentally, Russian cosmonauts were also wearing Speedmasters if they could get their hands on them – during the Apollo Soyuz mission in 1975, both flight crews were wearing Speedmasters.)  The recertification process took place once again, and, to quote Alan Nelson's excellent historical study of the Speedmaster:


Once again, the Omega chronograph was superior to the other chronographs tested. The Speedmaster Professional met all environmental requirements, had the highest technical score, and was offered at the lowest price. Therefore, the Omega was accepted for procurement. It is significant to note that this was the identical model, which had been submitted in 1962. The watch was offered to NASA at the cost of $0.01 per watch.


And in 1989, the Soviet Union heaved a collective sigh and made it official –selecting the Speedmaster as the official watch to be supplied to all cosmonauts.  That the watch was offered to NASA "at the cost of $0.01 per watch" clearly seems to indicate that NASA purchased watches in addition to the early, 1965 batch of cal. 321 Speedmasters (one certainly hopes so, otherwise Shuttle crews would have been flying with watches rather conspicuously outside the recommended service interval!)  It's therefore quite reasonable to acknowledge that while the current Speedmaster with cal. 1861 is not exactly the original Moonwatch, it is still a workhorse instrument repeatedly proven to be able to tolerate the rigors of operation beyond the surly bonds of earth.


Today, of course, with the aging and dangerous Space Shuttle reaching the end of its service life, and with NASA's stock in trade consisting largely of scientific missions to the planets in which incredibly sophisticated robot probes have taken the place of manned space flight (largely a sensible decision both from a cost and safety standpoint, it must be admitted) the Speedmaster, too, has largely been superseded.  The mechanical Speedmaster Professional has been supplanted by the X-33, an up to date quartz mechanical/analog watch designed, unlike the Speedmaster, to function specifically in aerospace activities (it includes a whole host of features included at the behest of the aviators and astronauts who participated in its design, including a multi-day mission timer, and alarms loud enough to actually be useful.)  Astronauts and serious military aviators today generally rely on quartz digitals, including the other two watches (in addition to the Speedmaster and X-33) that are officially flight qualified by NASA, the Timex Ironman and the Casio G-Shock.


But for me, and for others of my generation, the Speedmaster remains a kind of horological equivalent to Proust's Madeleine, a trigger for a cascade of memories and aspirations both personal and national, which are no less sweet for having largely given way to the pressures of changing time and age.  Like so many who grew up during those early days of the space race, I wanted more than anything else to be an astronaut, and though that ambition has long since fallen away, the Speedmaster's honest construction, rich history, and personal meaning makes it for me, and for many of my generation, the ultimate touchstone of horological authenticity.  Let other watches dress themselves in the tawdry robes of borrowed or inauthentic history; the Speedmaster has been there, done that, and lived (sometimes by the skin of its teeth) to tell the tale.  Age cannot wither nor custom stale her allure, which is more than you can say for most of her owners, so as the Speedmaster turns 50, let us all salute her, and wish her another 50 years of reminding us of where we've been, and where, perhaps, we might someday go again.




The Moon Watch: The First and only Watch Worn on the Moon, published by Omega SA


Apollo Lunar Surface Journal


W. David Compton, Where No Man Has Gone Before: A History of Apollo Lunar Exploration Missions (Washington, D.C.: NASA SP-4214, 1989)


Chuck Maddox's Speedmaster Articles (


Club Speedmaster (


"The Moon Watch:  A History of the Omega Speedmaster Professional" NAWCC Bulletin, Feb. 1993, Alan A. Nelson


JFK and the Space Race, Marc Selverstone, Miller Center of Public Affairs of the University of Virginia (


Antiquorum Archives and Omegamania Catalogue


Max Tegmark, "Parallel Universes," Scientific American May 2004

Jack Forster has asserted his right to be identified as the author of this work.
Copyright assigned to , May 2007. All rights reserved

This message has been edited by MTF on 2007-05-08 09:54:58 This message has been edited by MTF on 2007-05-12 22:39:28

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 By: Chromatic Fugue : May 8th, 2007-09:47
Jack, this is exactly the sort of lucid technical explanation of this watch that I've been hankering for, and it's simply fantastic! - Jon

Thanks Jon!

 By: Jack Forster : May 10th, 2007-17:47

Jack this deserves a standing ovation!! A Masterpiece!! Congratulations and Thank you>>>

 By: MARCOS : May 8th, 2007-11:30
This is a work to be in a book! Together with part 1. I enjoyed part 1 when you mention the "labia types", IIRC, that was funny! Best regards, Marcos

God Bless You, Jack! ;-) nt

 By: Chris Meisenzahl : May 8th, 2007-12:25

Hi Chris- just a little. . .

 By: Jack Forster : May 10th, 2007-17:49


 By: Moses : May 8th, 2007-15:23
Together with Part 1, a splendid achievement!

this revives a dilemma for me

 By: Chromatic Fugue : May 8th, 2007-19:12
I've been putting off buying one of these because I couldn't choose between the "traditional" Speedy Pro with the hesalite front and solid back and the "sapphire sandwich" model with the display back. Finally, in previous posts, Jack and John had both per... 

I'm also now interested in the 'sapphire sandwhich' but...

 By: Andy : May 9th, 2007-01:34
does anybody have any pics of the profile of the front crystal..?? I'd like to know if the shape is the same as the curved beveled edged plastic or if it is flat like on a Rolex for example. Outstanding report too.....any benefits to the plastic or metal ... 

Hi gents, I believe the crystal is domed on the sapphire as well. . .

 By: Jack Forster : May 10th, 2007-17:54
. . .it's a lovely watch, and the fact is that it's really value added to be able to ogle the works through the caseback. I think functionally the nylon brake actually slightly has the edge on the metal one (of course, I have no authoritative evidence of ... 

what Jack made me do ---

 By: Chromatic Fugue : May 11th, 2007-15:54
Got this earlier today: the classic, no display back, but I'm cool with that. I'll just bookmark Jack's article for easy access to the greatest article ever written on this movement. Thanks again, Jack!...  

CONGRATULATIONS!!!! Now all you need to do is perform. . .

 By: Jack Forster : May 11th, 2007-19:14
. . . the traditional ritual of new Speedmaster ownership. Rent "Apollo 13" and crack open a bottle of your favorite single malt (if you're me ;-) ) and wait with bated breath for the mid course correction burn scene ;-) . Or alternatively, play the Speed... 

I'll try the drinking game

 By: Chromatic Fugue : May 11th, 2007-21:44
and the only suspense will be whether I can write a coherent post afterwards. Looking forward to it!

Simply fabulous - Thanks Jack (nt)

 By: Velociphile - No longer in the building : May 9th, 2007-02:23

Avec plaisir, V. . .

 By: Jack Forster : May 10th, 2007-17:54

Thank you Ron!

 By: Jack Forster : May 10th, 2007-17:54
Look forward to seeing you in NYC again one of these days! Jack

Me too, Jack. (nt)

 By: Ronald Held : May 11th, 2007-05:16

Sensational, Jack! Incredible clarity, detailed pictures,

 By: SteveG : May 9th, 2007-07:14
comedic attitude, what more could one ask! thanks!

I can take credit for

 By: Jack Forster : May 10th, 2007-17:56

Jack, you just topped yourself!

 By: Valentin Blank : May 9th, 2007-07:56
Dear Jack Thank you so much for this wonderful article! I enjoyed every line of it and I learned a lot more about my favourite watch. For example, your notes about the dial are so enlightening. They explain what I have never bothered to measure/analyse bu... 

brilliant, nice job! (nt)

 By: ei8htohms : May 9th, 2007-18:43

Exceedingly well done Jack! I hope you have it archived!

 By: Chicagoland Chuck Maddox : May 9th, 2007-18:58
I'd be happy to host an archive on my site if that would be helpful! Cheers! -- Chuck

Chuck, this is one of the greatest compliments of my career as a horological writer. . .

 By: Jack Forster : May 10th, 2007-18:02
. . . you are universally recognized as THE definitive authority on the Web for the Speedmaster- and not just the Moonwatch but the various Marks in all their incarnations, and your resources are now and will remain for the forseeable future not only the ... 

It's well deserved, Jack.

 By: Chicagoland Chuck Maddox : May 11th, 2007-12:33

Simply outstanding!

 By: Rrryan : May 9th, 2007-21:43
Wonderful article, well-researched and beautifully written. Well done! If I might be so presumptuous to add one more detail, the material used for the chrono brake is more specifically known as Delrin. Regards, -r This message has been edited by MTF on 20... 

Thanks so much! I'd read it referred to as such. . .

 By: Jack Forster : May 10th, 2007-18:03
. . .but couldn't confirm it through the Omega tech docs I had to hand. Best regards, Jack

Even at a 2nd reading >>

 By: MTF : May 9th, 2007-23:01
it was just as good as the draft reading Thanks! MTF

Bloody marvelous, Jack!

 By: Laurence G : May 9th, 2007-23:27
I've spent the week reading up everything I can find about this legend and I might just buy one myself. That said, this opens up a thread of considerations like open-backed cases to collectors' editions as opposed to the regular models sold in the boutiqu... 

Great read - thank you [nt]

 By: MGM : May 10th, 2007-04:49
No message body

Great post Jack ....

 By: Bill Sohne : May 12th, 2007-11:39
Hi Jack i just want to say thank you for such a deep article. Out in the internet you do not come across this caliber of work too often. Best regards Bill Sohne

Ditto . . .

 By: Dr No : May 12th, 2007-18:12


 By: Kelly M : May 16th, 2007-21:46