A weight jack is a threaded adjuster at one corner of a race car that raises or lowers that corner's spring, moving load diagonally across the four tires. Turning one is what racers call putting in wedge.
Raising the right front and left rear adds cross-weight; raising the left front and right rear takes it out. Grassroots Motorsports gives the mechanism — raise a corner and that corner plus its diagonal opposite gain weight, while “the other two corners will lose weight” — and states the limit: “Jacking weight will not alter the left side or the rear percentages.” A jack bolt is a cross-weight tool, nothing else. Racers call one full turn “a round” — not a standard unit. What a round is worth in pounds depends on the spring rate at that corner, the motion ratio and the thread pitch of the bolt, so it does not carry from one car to the next. Every round moves ride height too. Write down what you turned.
A weight jack is the fastest handling change on the car and the easiest one to lose track of, because nothing on the chassis records how many rounds you put in.