I've come across a strange issue when trying to calibrate a HP34401A.
The DCV/DCRES/DCI cal is straightforward, but on the AC 100mV range there is a cal point at 10mV (10% of full range) and at 100mV.
Now the full range cal works as expected, but when I try to do the 10mV one it seems to have no effect. These are the steps taken:
1) Apply 10mV at 1kHz from calibrator (datron 4200) to HP34401A and HP3458A (Keysight calibrated)
2) 3458A (setacv sync, res .001, lfilter on) reads e.g. 10.0142mV, 34401A (filter slow/3hz, resolution 6 digit slow) reads 9.8654mV
3) Enter calibration menu, cal displays 100.0000mV
4) Set cal display to 10.0142mV and enter
5) 34401A displays cal 10mV AC
6) Display returns to measurement 9.8654mV (last digit changing due to noise as normal)
Now I'd expect after entering the cal value the 34401A would display, within the error margin of 45uV, the entered value but it does not, it's as if the calibration has no effect. Which is in contrast with other calibration steps, but all of them are at full range or near full range.
Am I missing something? The manual does not indicate anything different about this cal step.