The Pilkington & Gibbs heliochronometer was renowned for its accuracy with calculating mean time. In 1906 promotional material it was claimed to maintain accuracy to within one minute of true clock time. Around 1000 heliochronometers were manufactured by Pilkington & Gibbs between c.1905 and c.1913. Residual stock ran out c. 1922. No mental arithmetic was required to calculate mean time and it was usable across the world. Initially P&G sold directly to the public but later used various retail outlets. The heliochronometer was an assembly of about twenty finely machined bronze components with many screws and screw nuts. Details of how the P&G heliochronometer works may be found in the British Sundial Society Bulletin Vol. 18 (ii), article by Graham Aldred 'A Review of the Heliochronometers by Pilkington and Gibbs'