Quote Originally Posted by 3dkarma View Post
If you mean measuring the reference voltage or vref, the positive probe should be touched to the round metal circle to the right of the heat sink on the middle-right of your picture. The circle is the trimpot, which you turn to adjust the vref.
Thanks - that was what I was looking for - probably didnt explain myself very well - can the negative probe be earthed anywhere metal on the Printer ?