This imposing clock is one of only four of its kind known to exist. The 35cm square dial has indications for time, age, and phase of the moon, degree of the zodiac and annual calendar. The hour hand has a Sun disc attached and sunrise and sunset times are represented on the 24-hour dial by two sliding steel shutters moving up and down during the year.

A similar clock, presented to Queen Ann in 1705, was described as 'a very curious piece of clockwork', but it disappeared sometime after 1835. Although very similar, the evidence suggests that the Nation Maritime Museum's example is not the royal one.