It is a valid point about calibration. I have had a CT160 and now have a VCM163 and I have calibrated them myself. If Andy has just acquired the Mk4 it is a valid and important matter to find out when it was last calibrated.
Andy, assuming you are happy that it is calibrated or at least recently checked over to make sure it is working OK, then a little time with the manual should be enough to get you conversant with how to check a valve on the Mk 4. From memory it is similar to the CT160 in that it uses a 'backing off' method but it is quite easy once you get the hang of it.