Omega Observatory precision calibres
Grade “D”, 16 or 17 jewels, available as “chronomètre”, from size 13’’’ up to 20’’’ with a Bulletin de marche issued by the Bureau or the Observatory in Bienne, Neuchatel or Geneva; adjusted to variations of less than a minute per month, in 5 positions and under extreme temperatures.
Grade “DD”, very fine finished, 18, 19 and 20’’’.
Grade “DR”, extra-fine finish, 19 and 20’’’, with 19 jewels, balance screws in gold.
Grade “DDR”, appeared in 1905, 19 and 20’’’, intended for official chronometers and observatories, made in silvered nickel, with 23 jewels (incl. 2 diamonds), all parts polished and / or gold-finished.
· 19’’’ “DDR”, 900 pieces were made in 1906-1907 and 1911.
· 20’’’ “DDR”, 396 pieces were made in 1905 and 1908.
The 19’’’ “DDR” calibre was replaced in July 1922 by the Calibre 43.15, which was named “Verybest”, also equipped with 23 jewels; 600 pieces were made.
Until 1967, the exact duration of a second was determined by the Earth’s movement around the Sun. Thanks to the telescopes of astronomical observatories, extremely precise measurements were taken to determine the exact time.
In Switzerland, as early as the middle of the 19th century, scientists and watchmaking industrialists cooperated in chronometric tests. The Geneva and Neuchâtel observatories, for example, hosted precision competitions, the conditions of which would evolve with time and technological advances. In the course of the 20th century, these tests took place over a period of forty-five days and included ten separate tests to time the movement in five different positions and at two different temperatures.
These tests quickly exceed their function as simple certification tests and become a real competition ground for the best watch manufacturers in Switzerland and Europe. In Geneva, the names of H.-R. Ekegrén, B. Haas, Patek Philippe, Vacheron Constantin, etc., are regularly found there, and in Neuchâtel, those of Longines, Omega, Peseux, Ulysse Nardin, Zenith, etc., are also present.
This theatre gives rise to movements specially designed for these annual events, which have today become legendary calibres. Some watchmakers specialise in adjusting these movements; they are the precision timers (“régleurs de precision”); the aristocrats of the profession.
Precision movements are manufactured with much smaller mechanical tolerances than standard watch movements and often take as long to make and adjust as movements for watches with horological complications.
The Guillaume balance is a compensated bimetallic balance, made of anibal (an alloy of steel and nickel) and brass, after the works of Dr Charles-Edouard Guillaume (1861-1938), with which the middle-temperature error is practically eliminated.
The middle-temperature error (or Dent’s anomaly), is the difference between the rate of a chronometer at the mean temperature and the average of the rates at extreme temperatures.
This type of balance was used by the horological manufactories since 1904.