Sundial of the "helio-chronometer" type In bronze, engraved on the base. Months are indicated in English. Signed Pilkinson & Gibbs Ltd England, circa 1910 H. 25.5 cm - Diam. 22.5 cm Trace of label on back George James Gibbs invented and patented this type of helio-chronometer. Around 1,000 were manufactured by Pilkinson & Gibbs between 1907 and 1914. This instrument was renowned for its precision in calculating mean time, enabling time to be determined with a margin of error of around one minute. Details of the operation of the P&G helio-chronometer can be found in the British Sundial Society Bulletin, Vol. 18.