Chronometer NSN 6645-01-554-0609

An instrument for precisely determining time, manufactured to close tolerances to assure the time-keeping qualities of dependability and consistency of rate. These qualities are accurately ascertained by comparison with more exact devices or by astronomical methods so that the accumulated error may be taken into account when determining time. Its usual uses are to indicate time for navigational purposes, and to serve as a reference for less accurate timepieces. It is usually provided with a winding indicator dial and is usually mounted in gimbals to maintain the instrument in a level position. May consist of a spring driven or other type of movement which is capable of exacting performance without regulation throughout the normal range of room temperatures. Not designed for carrying on the person.