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Here, it is indispensable to spend some time on the definition of a Chronometer.
According to Mr L. Defossez, who published an article in the Société Suisse De Chronométrie, there was an evolution in the definition of a Chronometer:
- In 1714, the english watchmaker, Jeremy Thacker, was the first to use the word " Chronometer " for a marine timekeeper.
- In 1782, John Arnold gave this appellation to watches which used a detent escapement., and only for them.
So, basically a chronometer should have two attributes: Precision AND a detent escapement.
BUT watches with lever escapements started to achieve excellents results, too. So, watches with lever escapements were called " half chronometers " to distinguish them from those which used detent escapements ( and fusée, also ).
In 1900, the International Congress of Time Measurement, brought a new definition of the word " Chronometer ":
1/ Marine Chronometers fitted with the spring detent escapement ( Nothing new, here ).
2/ Pocket watches, fitted with the detent escapement, OR with the lever escapement, IF their mean rate is perfectly steady at room temperature, extreme temperatures, and at different positions. "
Different temperatures and positions, these are exigences we'll find on many wristwatches, but the question is to know if these virtues are enough to qualify them as Chronometers.
About wristwatches, we have to consider two eras: Up to 1951, and since 1951.
Up to 1951, the definition is the following one: " A Chronometer is a PRECISION watch regulated in DIFFERENT POSITIONS and at VARIOUS TEMPERATURES, CAPABLE of obtaining an official timekeeping certificate ".
In 1951, and since, the Federation of Swiss Watch Manufacturers changed the rule: " A Chronometer is a PRECISION watch ( aren't they ALL supposed to be precise, by the way? ) regulated in DIFFERENT POSITIONS and at VARIOUS TEMPERATURES, HAVING OBTAINED an official timekeeping certificate ".
Since then, and still nowadays, the word Chronometer is STRICTLY defined, and cannot be used if the watch in question is not accompanied by its certificate, delivered by one of the five testing stations: La Chaux De Fonds, Le Locle, Bienne, Saint Imier and Le Sentier.
Once we have these criterias and definitions precisely in mind, let's see what are the Vintage Lecoultre and Jaeger- Lecoultre which can qualify as Chronometer watches.
The watches which could be considered as Chronometers:
The watches delivered by Jaeger-Lecoultre to the US and British Armies had to be submitted to rigorous tests, as soon as the very first years of the Second World War.
According to the US Military Specifications, the movement ( mainly the Cal 450 ) of the US LeCoultre A 11- Weems had to be accurate from 20 to 45 seconds per day, depending on the postion and the temperature.
The Weems and its movement:
The same goes with the British Mark 7 A, by the way.
The Weems had a slightly bigger case ( 33 mm ), when the " No Weems " were one millimeter smaller.
The movement ( Cal 470 ) had to answer to some accuracy exigences: More or less 15 seconds per day, under different positions.
The Mark 7 A
:
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As said, we are, here in the early Fourties.
So, my opinion here is that the 1000 Mark 7 A Weems and the 4000 " non Weems " Mark 7 A which were in production may also be considered as Chronometers, since they were submitted to severe tests for the sole purpose of accuracy, in different positions and temperatures, such as the Chronometers were.
Therefore, we are before 1951, here, and the definition given by the Federation of Swiss Watch Manufacturers, which requires an Observatory certificate, doesn't apply to these former watches.
Hence the reasons which drove me to speak about these watches as Chronometers, even if the discussion is really open, about them.
I think we should also include the " WWW " and its movement ( Cal 479 ) which was totally dedicated to this watch, in the Mid Fourties, 1944, to be precise
10 000 Cal 479 were made, but only God knows how many " WWW " were in production.
The " WWW " and its movement:
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The watches which undisputably have to be considered as Chronometers:
Then comes the Mark 11, or should I use the plurial as they were delivered to the British and the Australian Royal Army Air Forces, for a total of 2950 watches, produced between 1948 and 1953.
Here, the movement, the Cal 488 SBr, has been submitted to the severe tests of the Kew Teddington Observatory ( United Kingdom ), and was the only one to receive a stop second among the Vintage JLC Military Wristwatches.
According to the MOD Specifications, the Cal 488 SBr had to be accurate within + / - 4 seconds per day.
The watch ( RAAF Mark 11 ), and its movement:
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A superb RAF Mark 11, with Cathedral Hands ( Credit picture: Zaf Basha ) :
Both the WWW and the Mark 11 had a bigger case, compared to the Weems and No Weems Mark 7 ( 35 mm ).
The case of the Mark 11 was in stainless steel, while the WWW had a chromium plated case, with a stainless steel case back
Two interesting details to add:
- Both the Cal 488 SBr, the Cal 479 and the Cal 470 share the same base, the Cal 450.
- The Cal P 478 BWSbr ( The movement housed in the ... Geophysic ) was an evolution of the Cal 488 SBr used in the Mark 11.
These Chronometer movements have to be seen as the roots, the source of the " Civilian Chronometry " in JLC wristwatches.