All springs have a Spring Rate. It’s the amount of pressure, in pounds, required to compress a spring one inch.
The machine in the photo’s foreground determines the Spring Rate by squeezing it down with a hydraulic cylinder. The dial indicator tells us when we’ve compressed the spring exactly one inch. The load cell at the bottom sends a signal to the digital read-out with the Spring Rate number. It helps us when we want to install stiffer or softer suspension springs in a car to alter handling characteristics, ride quality, ground clearance, etc.