Spring Scale Calibrated with Known Weights

A spring scale, or newton meter, is a spring fixed at one end with a hook at the other. By Hooke's law the stretch grows in step with the force, so the marks on its scale are evenly spaced. This one is built in a clear tube with a paper scale and calibrated with known weights: on Earth a 100 g mass pulls with about 0.98 N (100 g × 9.81 m/s²). The sizes here are ours: a tube about 20 cm long and a light extension spring that stretches clearly under 1 kg. Do not load it past the heaviest calibration weight: an overstretched spring stays longer and the scale is lost.