Movement Quiz #2: Guess the complication?

 By: skyeriding : July 20th, 2019-22:35
I've done this more than a year ago, now time for the second instalment!

What is the complication shown here? Bonus points if you can identify the movement and watch brand!

Image taken from khepri__watch_repair_horology, on Instagram.


Perpetual Calender or annual calender?

 By: Spencer Karrington : July 20th, 2019-23:46
I have no idea about watch mechanics so if I get this right, I will be very shocked

Close - it is calendar related - but not quite. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-01:00
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I will take that :) Thank you for your reply and I am excited to see what the result is [nt]

 By: Spencer Karrington : July 21st, 2019-06:08
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The correct answer is below! Thanks for participating. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-10:08
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I think its a day of month wheel with possibly a moonphase ? [nt]

 By: templetowers : July 21st, 2019-01:02
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Not a moonphase. "Day of month" is getting warmer, but there's something specific about this one. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-03:02
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A menstruation tracker!?!

 By: Spangles - Mr. Tabby : July 21st, 2019-09:21
"It's that time of the month!"

The answer is below! It'd be scary if the cycle was every 10 days... Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-10:09
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For if a month has 30 or 31 days? [nt]

 By: Spangles - Mr. Tabby : July 21st, 2019-02:09
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Good guess, but not quite! True there is ~31 teeth on the wheel, but its something else... Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-03:03
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I know the MIH has a strange system,

 By: thegrailwatch : July 21st, 2019-03:00
is it the calendar system from that?

Not the MIH; that one uses a weird shaped tiny gear. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-03:04
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Me Trying Again...

 By: thegrailwatch : July 21st, 2019-07:19
Tides Complication... belonging to Corum?

Nothing that exotic - the answer revealed below! Thanks for joining. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-10:09
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It has to do with a 24h circle, because of 24 teeth

 By: COUNT DE MONET : July 21st, 2019-03:31
However, every eight teeth a different tooth design.
A complication every 8 h ...?
It is not a moon phase wheel, that is clear.

Regarding brand: looking at the decoration and finish, it is a Swiss brand but nothing like Patek or VC, ... something less expensive.

Not 24, but ~30. "Every 8 hr' - the idea is good, we are close now. Brand analysis is accurate too. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-05:27
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Solunar? [nt]

 By: ektaylor : July 21st, 2019-06:32
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Unfortunately not. To clarify, its the idea that "every fixed number of teeth has a different design" thats important. But the timescale of 8hours is wrong. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-07:02
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O k., it is more like 9 teeth are the same and the 10th is different? [nt]

 By: COUNT DE MONET : July 21st, 2019-08:10
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Ok. There are nine spaces between the different gears, which means one wheel is counting 1 to 9. There are 4 “different gears” which means there's another wheel on top (or underneath) counting digits from 0 to 3.

 By: ektaylor : July 21st, 2019-08:15
It’s a digital day of the month indicator with separate wheels for the first and second digits. No idea who the manufacturer is.

I can see only 3 different ones [nt]

 By: COUNT DE MONET : July 21st, 2019-08:26
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Answer below! Admittedly the image isn't clear enough, I suspect it might even be missing due to forced damage and thus is in this pic for repair! Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-10:19
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And we finally arrive at our answer!

 By: skyeriding : July 21st, 2019-10:06

It is indeed, a bigdate complication, which has separate discs for each date digit. This particular version is found in Zenith's El Primero bigdate movements.

Image from:

Lets call the gear in the photo as the "central wheel". Unfortunately the image is not so clear and is taken from top view, so it is difficult to see the different level of gear teeth. However, you can find the patent online, here:

The key to guessing the complication is as ektaylor states, observe the central wheel has nine spaces between a set of extra teeth, which are sitting on a higher level. Precisely, there are four teeth on the upper gear which switches the tens digits, while there are 30 teeth on the lower gear which links to the ones digit.
Remark: I believe in the photo, one tooth may unfortunately be missing. It could be due to forced damage or something, which may be why its sent for repair!

The next observation is the two pivot hubs to the left and right of these wheels. They are meant for the ones and tens digit respectively.

What is not shown in the original photo, is that the mechanism is driven by an auxiliary disc (which is traditionally the regular date wheel) on the periphery of the movement, (14) on the patent image. This disc drives the ones digit, which in turn drives the central wheel and eventually the tens digit every ten days. Now, this disc is special - it is meant to have 31 teeth, but one is missing, this causes the ones digit to "skip" when date changes from 31->01.

However, note the Zenith uses a unique design where the tens digit has two "3" - it changes for both day 30 and 31, even though it doesn't need to. I presume the reason for this is so that the size of the ones and tens digit discs can be made the same size.

The upper central wheel with four teeth changes the tens digit on 09-10, 19-20, 29-30, 30-31. So how about the fifth and final change from 31-01? It actually does this directly via the auxiliary disc, which has an empty notch so it doesn't drive the ones digit, but instead has a tooth that directly drives the pinion of the tens digit from 3->0. This is because the final 3 digit has an extended tooth on the pinion, just long enough to be impulsed by the auxiliary disc. See (44) below image of patent.

Also note with this setup, the tens digit is geared at twice the speed of the ones digit (sweeps 1/5 a rotation instead of 1/10).

I hope the answer isn't too anticlimatic! A bigdate is not exactly an exotic complication...


Well done for this quizz! Very interesting and great to challenge our minds on technical questions!

 By: eklektik : July 21st, 2019-12:52
I am a bit chocked by the "dirtiness" of the main plate. Is that an old movement? Zenith should produce systematically with higher quality nowadays with decent numeric machines.

I am unsure, but the original poster of the photo is a watchmaker repairing/servicing movements, so it might be an old movement due. But it looks clean to me. Regards, skyeriding [nt]

 By: skyeriding : July 21st, 2019-16:11
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Sorry I don't mean dirty as such, but not executed at the highest standard. The machining marks are very uneven and are far from today's level of basic achievement. Best, É. [nt]

 By: eklektik : July 22nd, 2019-05:56
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I wouldn't have guessed! Thanks for the interesting post, my friend. [nt]

 By: amanico : July 21st, 2019-13:50
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Tidal complication? [nt]

 By: dedestexhes : July 21st, 2019-08:07
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Yes must be that. Heuer Mareographe? [nt]

 By: jlc.thomsen : July 21st, 2019-09:26
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