To begin using a spring scale, you should obtain two identical scales, as you want to use a spring scale with a partner for the best results. Begin by having holding onto one of the spring scales and having someone else hold the other. Then, hook the two scales together horizontally by aligning them hook to top. You do not want to align them in a hook-to-hook manner, since doing so makes it difficult to compare the readings of each scale.
Next, along with your partner, pull the spring scales in a back-and-forth fashion so that each spring scale reads the same value. This is the time to determine what the acceleration of each spring scale is. In addition, you also want to figure out what the net force on the two scales is. You should notice how the scales appear to be at rest and stay this way due to their acceleration being zero, which you probably already know due to making this determination in the last step. This means that the net force is also zero based upon Newton's Law. The scales do not read the net force, meaning that figuring out this piece of information depends upon the acceleration reading.