A bronze helio chronometer, early 20th century

Heliochronometers are an advanced form of sundial that are capable of extremely accurate time readings. Until 1880 time was local for each major city in the U.K. with Bristol being 4 minutes different to London for example. With the expansion of the railway network during the 19^th Century British time needed to be standardised for timetabling and in 1880 Greenwich time was adopted as the official time for the U.K. The difficulty was that there was no truly accurate way of establishing time unless you had access to the railway telegraph system.

In 1907 George Gibbs patent for a heliochronometer, which was accurate to within one minute, was accepted and he started to produce them along with William Pilkington. The design was ingenious as the date was "dialled in" and then a time reading could be taken whereas with conventional sundials time had to be worked out mathematically with the "Equation of Time". One other firm is recorded as having made heliochronometers to a very similar design namely Negretti and Zambra. In 1924 the B.B.C. started to broadcast time signals and the heliochronometers became obsolete.