Dirtdad, Just about any scale that measures weight can be positioned at the right spring height under a solid object, like a beam in the garage or basement, can compare each spring you squeeze between the scale and solid object. The scales pad may need a larger flat plate set across the pad so that it does not deflect in the concentrated area that the spring is on so that the space between the scale and solid object does not change when loaded. The method may not be exact yet it can tell you exactly if one spring is stiffer than another spring.