Clutch Slip Calculation uses 2 Inputs:


1) Engine Speed (RPM)

2) Input Shaft Speed (RPM)


Example.


Engine Speed = 6000

Input Shaft Speed = 5756 RPM


Clutch Slip(%) =   Input Shaft Speed - Engine Speed

                               Engine Speed


Clutch Slip(%) =  -4.06 % 


This means the Input Shaft is rotating 4.06% slower than the Engine Speed... i.e 4.06% Clutch Slip.