CAT Scale weights are confusing me.

The WD will raise the tongue and off load weight to the trailer axles in an effort to place weight on the steering and level everything out. It essentially shifts weight back on the trailer. Spring loading the arms puts pressure on the hitch point. This turns the ball into a type of fulcrum point which, for lack of a better term, lifts the back of the truck shifting weight to the SA. There are long explanations that can be found if you are interested in all the physics stuff.