They are the spring tensions at different compressed heights. Bigger #'s mean more tension. You can use them to tune engagement RPM and final rev RPM's (there's so much more to it than just that - weights, weight placement, clutch type, motor RPM band for peak HP and torque) but basically that's what they mean. Bigfoots link is good, some are measured in metric units (kg/cm2?) Ski Doo lists them in both.