Out of curiosity, are you also able to measure the analogue voltage coming out of the Kanalog? I was looking at my CSMIO+HY VFD combination yesterday. According to Mach3, the demanded speed was 15000; the VFD said 15500. Error of about 3% - not a big deal, and I can't think of many situations where that would matter to me. I would expect the spindle speed to track that pretty closely, given the motor technology and the fact that the motor speed display will be derived from the VFD digital electronics. When I did a similar test while initially configuring the machine, I seem to remember that there was a slight error in the analogue output from the motion controller which probably explains any discrepancy but I'm not sure I would trust my Maplin digital multimeter that well anyway.

But it's nice to know that it does what you expect! As for current readings - as Nick suggests, you don't know exactly what and how they are deriving these numbers, but it might be interesting to compare off-load and full-load readings.