Dial Spring Scale with Tare Screw: Fray & Pigg, 1881

John S. Fray and Horace Pigg of Bridgeport, Connecticut, patented this weighing scale in 1881, US 243,539. A dish sits on the standard of a frame hung on two pairs of cross-arms, so it moves straight up and down. A coil spring on a right-angle lever carries the load, and a rack on the frame turns a pinion carrying the pointer round the dial. To take up the tare, a screw rod through the front of the case moves the lever's lower end. Because the spring hangs vertically from the lever's horizontal arm, the adjustment is more sensitive and the bearing surfaces fewer.