Jaeger-LeCoultre Duomètre à Quantième Lunaire Caliber 381

Nearly three years have passed since Jaeger-LeCoultre presented the Duometre a Chronographe. This extraordinary piece was the first of an expected series of interpretations of horology devices powered by two parallel barrels. As you may know now the two barrels power two separated wheel trains, each of them having its own function.

In the Duometre a Chronographe one barrel and wheel train was used for indicating the time (hours, minutes and seconds) and the other was doubling the function on a chronograph way. Obviously both wheels trains were regulated by the same escapement. You may find more information about the way it works in this article I wrote at that time to explain it: jlc.watchprosite.com

In the Duometre a Grande Sonnerie, second Duometre and master piece of the Hybris Mechanica presented in September 2009, one barrel powers the Grande Sonnerie while the other powers the time indicators and the perpetual calendar.

This year Jaeger-LeCoultre presents another smart use of the dual wing concept with this calibre 381 of 369 parts. The Duometre a Quantieme Lunaire is a simpler watch in a sense, dedicated to precision and showing a very beautiful finish like the former Duometre.

Jaeger-LeCoultre Duometre a Quantieme Lunaire in yellow gold

Don't take me wrong ! I don't write "simple watch" meaning that it is made simply. This watch has a very well thought construction, quite inventive in fact. It uses a complicated way of expressing indications generally simple to realize, but for a good reason.

This watch shows the hours and minutes in the upper right part, the seconds hand at the centre, the sixth of a second at 6 and the date and moon phase and age at the upper left.

Dual barrels

You may wonder which barrel powers each of these indications?  Well in fact one barrel powers them all!

Is there any use for the second barrel? Yes, it powers the escapement.  Why? Because if one barrel powers only the escapement, its flow of energy is not perturbed by the needed energy for the indicators like in other watches. This is the Duometre principle we already know. It was the same basic principle with the Duometre a Chronographe: being powered by another barrel, the use of the chronograph train had no interaction with the precision of the time indication.

Permanent lightning second

In the Duometre a Quantieme lunaire the energy needed to move the indicators of the hour, the minute, the second, the sixth of a second, the date, and all the moon indications, is not taken from the energy that powers the escapement. Consequently the flow of energy at the escapement is directly depending of the torque curb of the barrel. This is not a constant force escapement, but it is an isolated escapement (isolated from the inertia of the indicators).

This is the first positive aspect of this dual wing construction (and the difference from the Duometre a Chronographe).

Precision is the aim

Precision relies in the indication too. The clear and separated indicators help improving the precision of reading.

Open dial

The second main positive outcome of this construction relies in one major aspect of all precise watches: it hacks!

But contrarily to traditional watches when the Duometre a Quantieme Lunaire hacks the balance wheel is not stopped. All indicators are stopped but the escapement keeps running perfectly and that way the use of the stop seconds function has no interference on the balance amplitude and frequence. The precision of the timing is totally preserved from interference from the setting of indicators.

The balance wheel is 10mm large and has an inertia of 11.5 mg cm2. It beats at a frequency of 3 Hz or 21 600 vph. I'm particularly fan of these large and heavy balance wheels running at moderately fast speeds. Fast balance wheels have their advantages too, but they are generally small and light to preserve the power reserve. Here we have a sufficient power reserve of 50 hours. A manual wind aimed at running at the best of its torque curb deserves a daily winding in my opinion.

Pink gold is fashionable these days

To sum up we can consider that if the escapement is properly regulated, the long term use of the watch has no consequence on its precision: setting the indicators or hacking the watch to synchronize the second doesn't act on the precision of timing of the escapement. Only the torque curb of the escapement barrel can influence the precision. Still it is known that a spring can have a range of use with a pretty steady torque before the torque changes. You have to use that part of the spring for the best timing.

I still have to ask and get from Jaeger-LeCoultre the information about the torque curb principles of this calibre but I guess that the smart use of the power reserve indicator can lead to a very precise watch. I also hope to get more information about the precision tolerances of this watch. Of course the SIHH is just over and we have to be patient but I'm sure it will come sooner or later.

A complicated aspect for a simple watch

As I wrote about hacking the watch, in fact I must explain. If you pull the crown it stops the seconds hand immediately and the lighting seconds hand keeps running till it stops at 0. The other indicators are stopped too but you obviously can't notice it. If you pull again lightly the crown the central seconds hand goes back to 0, pushed by a heart cam like those used for resetting chronograph hands.

Once you push back the crown at the desired moment the hands and all indicators begin running again. At this precise time the escapement is still at full precision as it was not stopped and is not interfered by the re-activation of the indicators.

Perfect on my wrist

There is another positive aspect of this watch construction. The lightning seconds hand is permanently running (when it is not hacked of course) and this brings a very pleasing animation to the dial. We can sometimes regret to look at some very beautiful but "dead" dials of fantastic watches. This one is always alive and you have nothing to do to keep it alive, except keep an eye from time to time on the two power reserve indicators in the dial apertures.

Furthermore the sixth second hand is a natural indication as the escapement runs at 21,600 vibrations per hour, i.e. 6 per second!

Dial side

At first sight I regretted two things on this watch.

I didn't like the apertures on the dial. I generally don't like apertures showing the calibre. Honestly I've been fast to get used to these ones. They are limited and show interesting and nicely finished landscapes: the two power reserve indicators that appear on the opposite of the barrels, what I find amazing, and the balance wheel on the left, confirming that it doesn't stop while you hack and set the indicators.

The other point that I didn't like was the decoration of the moon disc. Don't worry it is not the definitive one that is pictured here. Although it looks nice on the two press pics, it was far from being as nice on the prototype watches I've seen, and I can't wait to see the production piece. About the moon indications I should precise that it relies on a classical 59 teeth wheel and consequently the moon will require a one day setting every three years. The moon is adjusted through a pusher at twelve while the date is corrected with the button at 10.

The face of the moon

This gorgeous watch will have a limited production of 300 pieces in yellow gold (26 500 euros expected) and will be un-limited in pink gold (25 500 euros expected), although production of Duometre models is not high enough to see one at every corner.

The case is 42 mm large, 13,5 mm thick and nicely filled by the 33,7 mm large and 7,5 mm high calibre The watch is waterproof at 50 meters. I have no idea of the waterproof capacity of the alligator strap though!

A totally new design

All in all this watch is a very appealing new offer. It has a very beautiful case, a gorgeous calibre, some very appealing chronometric virtues and promises (yet to be confirmed of course by figures). The functions are simple and useful, but also romantic with the moon and pressing with the lightning seconds hand! This watch is alive and wants to keep your time best than ever! I'd like to lend her mine, for sure!

Could that watch be my favourite current Jaeger-Lecoultre? Sure!

Cheers

Dje