Hines' 'Patent Weight and Quantity Calculator', c 1908.
© Science Museum / Science & Society Picture Library
Mechanical ready reckoner patented by Patented by James Hines. This form of calculator gave costs of various quantities of goods at various prices per pound, hundredweight or ton. The quantity was set by turning the appropriate wheel at the side, and the price per unit by using the keys. The cost would then show in the apropriate window.