Dino,
well it doesn't check the calibration as much as it checks for a certain expected voltage when the handle is in the neutral range.
Here are the voltage ranges for the travel pot, this may be of some help.
Full Forks First = 2.75 - 4.75
Neutral = 2.0 = 3.0 (the ideal setting would be around 2.5v)
Full Tractor First = 0.5 - 1.75

I could try and explain how to get into the TMM so you can run a learn on the handle but if you've never done it before you would need some first hand (someone present),guidance the first time. It would be best if you had someone that's worked on these or Raymond trucks before (these are the same), and/or call a cat tech out.
And if you ever decide to change out the VR1 you defiantly would need someone that's done it before.

Good Luck