steam,
Some of the 1st generation Z4K's had different read out fine tuning problems, I have one that is actually 3 Volts lower on the digital reading than the actual voltage being delivered to the tracks. I set it at 21 to achieve 18 on the tracks. I will probably never have it digitally fine tuned, I run DCS with that transformer all the time any way, and I purchased the Z4K from a OGR member at a very good price because of the digital problem. The Z4K operates perfectly other wise. If your Z4K operates properly for actual running, I would not bother to have it fine tuned.
PCRR/Dave