Double longcase clock

Solar sidereal long-case clock, purchased in 1716 by the Royal Hospital for Seamen at Greenwich for its Council Room, though only paid for (£70) in 1718 owing to initial dissatisfaction with its performance. One of only three of its kind known to exist, the clock has two separate, pendulum-controlled movements. The dial on the left shows sidereal (star) time, as used by astronomers, and the dial on the right shows mean solar time (GMT). The central dial at the top shows the day and the month and indicates the Equation of Time - the difference between solar time ('sundial time') and mean solar time ('clock time').