6" bellmetal rule engraved "Joseph Whitworth, Manchester, standard at 62 degree fahrenheit," part graduated to 64ths, c 1850

The bell-metal rule by Joseph Whitworth, Manchester, reflects his insistence on accuracy, being marked 'standard at 62 'Faht’. It is marked in fractions of an inch rather than decimal parts; measurement in decimal inches was strongly advocated by Whitworth.