Vehicle constants tab has 10 user definable vehicle constants for use with User Defined Variables.
The most common use of the car contants is to allow the user formulas to be dependant on the Vehicle. For example if you have data from 2 cars loaded, but with 2 different calibrations for the throttle then we could enter a user equation of:
Throttle = CAR_01 * x + CAR_02
And then enter the throttle gain and offset into the car constant table, a different values for each car as required.