[Test-Equipment] Help Request - HP 410C Calibration

[Mike Hardie]

My HP 410C VTVM won't calibrate on the .5 vdc and higher scales, A3R30 is
"hard over" counter cockwise with the meter reading slightly higher than it
should, 5.2 vdc when it should be 5, similar on other scales.

A3R21 is full counter clockwise plus 20 degrees as per the cal instructions.
The 3 lower vdc scales seem OK although A6R18 is near the end of travel.
The voltage standard is homebrew but appears accurate.

Any help will be greatly appreciated.

Mike VE7MMH