This impressive high-precision deck watch is double numbered on the movement and therefore it is likely that it was destined for Observatory timing trial. Like those of other makers, the movements of Longines watches were double engraved with the movement serial numbers when the intention was to submit them for testing. Deck watches were navigational instruments and as such had to be extremely accurate with a known rate of variation. The present two-day going watch has a free-sprung balance spring meaning that the watch has no manual regulator and can therefore only be fine adjusted by a watchmaker. Only watches with superior timekeeping properties, already tested and regulated by a master watchmaker are made free-sprung.