Nagra III - how to calibrate

[Vladislav81]

Hello, it's me again. In addition to tube Telefunken M5, I have Nagra III BH (broadcast version with 3 heads with no pilot). Now it's being repaired, replacing the belts with the new ones. 

The question is how to calibrate Nagra III. I'd like to know how to do it so to tell the technician.

Hope you would help me.