How do you measure the strength of the clutch springs?
Remove one clutch spring. Your 'installed spring height' is from the bottom of the pocket in the pressure plate, where the spring sits... to the top of where the spring sits. If your bike has a flat washer holding the spring - measure to the top of the post sticking up. (use the depth end of a set of dial calipers) If it has a ' Top Hat' - it would be the height of the post, plus the additional height of the top hat, added together.
Once you have this height. Let's say it's 1.04 in. (ZX-14R) You simply use the Rimac spring tester to measure the spring force, at this height, for a given spring or spring/shim combination. Add shims or washers (keeping the height the same) to see how much additional pressure is gained. (multiply by 6 for total spring pressure).
NOTE: NEVER compress a spring to solid, it ruins them forever.