Precision Laboratoy scales were first described in 1798 and became widely available around 1830. They are basically balances with delicate, sensitive mechanisms to increase precision. From the mid-1800s they were usually enclosed in glass paneled hardwood cases with sliding or hinged front or side doors for easy access and included a drawer for weights, tweezers and other accessories. Pans on precision scales are usually brass or nickel brass and can be quite small. The balance beams usually have a fixed or separate link with a small, sharp brass ridge hanging at the bottom. The wire loops that hold the pans have a separate link called an ‘agate box’, which contains a small bar of agate carved with a groove to fit delicately over the brass ridge. The ‘rider system’, which appeared around 1850, is an overhead beam equipped with wires and hooks to add minute amounts of weight for high-precision measurements. ‘Single pan balances’ introduced in 1947 speeded up weighing through a system of hand operated cams that lowered or raised weights. Microbalances, that operate with a quartz string which twists proportionally to the weight added were described in 1956, and electronic balances soon rendered mechanical chemical balances largely obsolete. There are many specialized laboratory scales designed to weigh specific objects. Some of these are in the Opticalia Museum.