1. Consists of a mirror scale 12 cm. long and supports spring, a weight holder and slotted weights of 250 gms. capacity.2. This complete apparatus has a 15 cm. adjustable mirror scale, to prevent parallax error, and is graduated in millimeters and mounted on sturdy 30 cm. support rod. A hook supporting a coiled spring with a mass hanger and indicator is attached to the rod. Supplied with slotted weight of 250 gm. capacity.