WEIGHING MACHINES

The commonest and most accurate type is the equal-armed balance—a beam supported in the middle and carrying at each end a scale pan. The beam is rested upon polished planes by means of knife-edges of hardened steel, and the scale-pans hang by chains from hooks also resting upon knife-edges. The beam should be ~ horizontal when the pans are removed, and these, with their chains should be exactly equal in weight. Other things being equal, the longer the arms of the balance, the smaller the weight of the beam; and the nearer the center of gravity of the beam to the point of support the greater will be the sensitivene of the balance. For retail trade purposes, where rapidity is more important than Ininute accuracy, the counter machine, which has scale-pans above and resting upon two beams cast in one piece or locked together, is most convenient, giving free acce to the scale-pans.