Here's why:

* Spring scales work by measuring the amount of stretch or compression in a spring. This stretch or compression is directly related to the force applied to the spring.

* Force is a push or pull. It's what causes objects to accelerate or change their motion.

* Weight, a common measurement made with a spring scale, is the force of gravity acting on an object's mass.

So, while you might use a spring scale to indirectly determine an object's weight, the physical property it directly measures is force.