A watch beats the Moon

The Board of Longitude sat down to consider John Harrison's sea watch, which had crossed to Jamaica and back and lost a few seconds, and decided it worked.

The rival method was the Moon: measure its distance from a star, look the angle up in a table, and read off Greenwich time. Lunars were free and needed no machine, but they took four hours of arithmetic and a clear sky. Ships carried both for another century, and the watch won because it could be read in a fog.