Have the same problem with pressing both buttons simultaneously especially when I want to see the mV during calibration. I like the way the meg deals with this:
When you select "Calibration" it displays a direct readout of all cells and only saves calibration data, when you confirm.

This could be adapted to the pursuit as well: upon selecting "calibration" just display the mVs instead of the PO2 (which at the time of calibrating is rather useless info IMHO).