What does a chronometer measure?
Marine chronometer such as Galileo's method based on observing Jupiter's natural satellites, was usually not possible at sea due to the ship's motion. The lunar distances method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer. The Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530. The purpose of a chronometer is to measure accurately the time of a known fixed location, for example Greenwich Mean Time (GMT). This is particularly important for navigation. Knowing GMT at local noon allows a navigator to use the time
Observatory chronometer observatory chronometer and received a Bulletin de Marche from the observatory, stipulating the performance of the movement. Of the millions of watches produced in Switzerland each year by all manufacturers in the mid-1960s, approximately 250,000 would receive official chronometer status (similar to what would be COSC standards today), and only a few hundred of the very best from the total production would be sent to an observatory for chronometer accuracy competitions. Watch movements that could compete for accuracy certification at the observatory had typically been specifically built for that purpose alone, they were slow beat movements, oscillating at from 18,000