This is a force meter. It is used to measure forces. The spring inside it stretches when pulled and there is a scale in Newton that shows the force applied to it. Springs are elastic, because they go back to their original shape after being stretched.
When you first hang something on a force meter, the forces are unbalanced, so it begins to stretch. As it stretches, it produces a bigger force pulling the object towards itself until the forces are balanced and the stretching stops. Then you can see the weight of the object.
Robert Hooke was a famous British scientist whose work led to the invention of the force meter. The unit of the force though, Newton, was named after his rival scientist Isaac Newton!