has never been seen as available on the open market, although it does appear in Omega literature but appears cosmetically identical to the calibre 1516 but with a 1510/1511 circuit, however Omega didn't produce a non Marine Chronometer/ Constellation in the smaller case type and as such it is highly unlikely the 1515 went into production watches. The calibre 1516 movement however was different in design to the 1511, specifically around the main-plate, which was reduced in the size of the movement by 5mm to be able to accommodate the movement in a newly designed smaller Marine Chronometer case. The components of the movement remained fundamentally identical to those of the previous 1511 Marine Chronometer however the screws holes on the main plate (to attach the movement to the case) were removed and replaced by a more traditional movement clamping system. The case design for the calibre 1516 looked cosmetically identical to that of the 1511 series and used the same 1209/202 integral bracelet, however it was a smaller watch in terms of height by 5mm and included the addition of a sapphire crystal (which had previously been mineral in the calibre 1511). The bezel on the 1516 was also bonded to the case and the 4 screws are purely cosmetic. The 1516 also had a slightly different positioning of the number plaque. The 1516 Marine Chronometer was produced in 7000 units and sales ran between 1976 and circa 1980, by which point the watch had priced itself out of a much more competitive quartz market and changes in fashions and watch design had limited the Marine Chronometers marketability. Of the 7000 examples of the 1516 Marine Chronometers made approximately 10 examples were made in 18K yellow gold with integral yellow gold bracelet and 18K white gold plaque and bezel. There are currently 2 known examples of the 18K Marine Chronometer in private hands. The 18 carat watches were commissioned and the cases produced individually by the Fontana factory in Italy. The 18K integral bracelet was identical to that used on the earlier 18K calibre 1510 watches. 4.19 MHz Ships Marine Chronometer In 1978 the French Naval Hydrographic and Oceanographic Service (French: Service hydrographique et océanographique de la Marine or SHOM) requested a Quartz Ships Chronometer to acquire a reliable autonomous time source independent of external satellite and radio signals. The goal was a timepiece for navigational purposes, like establishing