A spring is attached to a clamp which is secured to a bench.The initial length of the spring is recorded then a range of slotted masses are suspended from the spring and the length is again recorded. The extension is the change in length.The accuracy is improved by using a set square and reading the lengths at eye level to eliminate parallax errors.Repeatability can be checked, and the effect of random errors reduced, by taking three readings each at six different masses and calculating the mean.