The National Maritime Museum specializes in precision timekeeping. With over 1000 objects, it is the finest collection of its kind in the world. The collection includes precision pendulum clocks (regulators), marine chronometers and deck watches. Especially notable are the famous and seminal series of timekeepers by John Harrison (1693-1776). Time distribution devices include the original Shepherd master and slave system, the famous time ball by Maudsley on the Royal Observatory, Greenwich roof and the original regulators generating the BBC 'six-pip' signals.