This astronomical regulator was originally made for use in observing the Transit of Venus in 1874. In 1923 it was adapted as the primary standard for the new six-pip time signal. The clock sent electrical impulses down a telephone wire to the BBC for conversion into audio pips for radio broadcasts. It has a zinc tube temperature-compensated pendulum and was corrected from 1929 by the Shortt master clock number 16. The three sets of contacts for closing the six-pip circuit every quarter of an hour can be seen in two of the holes within the seconds dial, and halfway down the pendulum, operated by a roller.

This clock was in service for the BBC signal at the Observatory from 1924 to 1949, when it was superseded by a quartz clock.