Picture Number:10314157 Credit:Science Museum/Science & Society Picture Library
Chinese steelyard balance with ivory beam, brass pan and counterpoise, dated to the19th century. Commonly called dotchins these scales are usually stored in wooden cases shaped like a banjo. Working on the lever principle the dotchin operates by moving the rectangular counterweight along the beam until the item being weighed is horizontal and hence in equilibrium. The weight is determined by the position of the counterpoise thread against the lines and divisions marks on the balance beam.