Open Settings to match how many pounds one tandem hole and one fifth-wheel notch move on your rig. They are saved on this phone.
Sliding the trailer tandems back (toward the rear of the trailer) moves weight off the tandems and onto the drives. Sliding them forward moves weight off the drives and onto the tandems.
Moving the fifth wheel forward (toward the cab) moves weight off the drives and onto the steer axle. Moving it back moves weight off the steer and onto the drives.
The common federal limits are 12,000 lbs steer, 34,000 lbs on the drive tandem, 34,000 lbs on the trailer tandem and 80,000 lbs gross. Your steer limit may also depend on tire ratings, and states, bridges and permits can set different limits, so always check state and local rules for your route.
The trailer slider rail has a row of holes, usually a few inches apart, that the locking pins go into. "Lbs per hole" is how much weight moves between the drives and the tandems each time you slide one hole. About 250 lbs is typical, but it varies by trailer and load.
A sliding fifth wheel locks into notches along its rail. "Lbs per notch" is how much weight moves between the steer and the drives for each notch. About 500 lbs is a common starting point; check yours against a scale ticket.
If the gross is over 80,000 lbs, or the load is too heavy at one end, no slide will make it legal. The calculator will warn you, and the load needs to be reworked or reduced.