Calculation of the trim gain

I would like to know the formula to calculate the decimal value (0/1) of the trim gain of each slot (Kit > Tech General > Trim) (-infinite/+6db). Any idea ?

XML : <BFD2KitPiece name=“kp_slot_0” pan=“0.5” trim=“0.8” dampAmt=“0” dampFreq=“500” …>

So, nobody know how to calculate it ?