Calipers
Compasses having two curved legs or fingers pivoted together and used either to measure the inside or outside diameter of bodies. Calipers are divided into two classes, known as inside and outside calipers. They are used by watchmakers for determining the diameter of staffs and pinions, for testing the truth of wheels, etc. Calipers are sometimes used in poising balances, the balance staff being centered between the points of the calipers. For this purpose a hole is drilled in the calipers and jewels are inserted. Thompson's jeweled calipers, shown in Fig. 46, have garnet jewels inserted in the points of the arms at one end, and hardened steel bearings in the other. The Euclid Double Calipers are very useful tools, as they give on the lower limbs an inside measurement corresponding to the outside measurement of the upper limbs. By adding a stop screw to the common double calipers as shown in Fig. 47, a very handy tool can be made, as the tool can be opened and removed from the work and closed again exactly the same amount. See Gauge. CALLET, F. A thorough mechanic and skilled calculator. He was born at Versailles, France, in 1744, and died in 1798.