DMM linearity comparison

[Kleinstein]

If the DMM uses a separate gain and offset for both signs, than part of the INL problem could be from a not so ideal calibration. For later use one does not really care why the DMM causes an error. Ideally there should be no breake in the gain and offset, as the ADC also works in the range across zero. The region around zero is often the most critical one, but the critical point may as well be a few mV off 0 V and a change in gain offset thus is more like a dangerous correction that can add another discontinuity at zero.

The Fluke calibrator should have some internal parameter for the offset and this would effect the polarity reversal. So I somewhat understand that some correction here may make sense. However this would be only an offset shift, not a change in the gain.