This is a drilling jig that is intended to help guide drill holes for adding tungsten weights to the bottom of a pinewood derby car. The default settings are setup for 3/8" diameter weights, and distributing the holes on either side of the shorter of the two axel lengths on the block. You can use the tool to drill 1 or 3 holes in front of the axel and optionally do the same behind if more weight is needed. On my son's car we did 3 in front and 1 behind.
Use the slot to ensure alignment to the axel channel on your block, then clamp it to the body. Add tape to your drill bit once you've determined the depth you need (for the number of weights you are adding, and the depth of the jig).
If you want to flip your car backwards or custom, you can change the axelDistFromRear to the measurement you want.