“Assuming that initial calibration value of 7 was incorrect, and the new calibration of 12 was correct for the given temperature, etc, then your power meter would have been over-reporting your watts while the calibration value was 7”.
Thanks, that’s all I was looking for, but lots of good tangential info in this thread.
Also, to clarify the scenario: I usually wait until after the warmup to do the calibration. I understand that temperature differences as the workout goes on should theoretically be taken into account automatically if I were to calibrate at the beginning of the workout, but I figure it can’t hurt to calibrate after everything is warm (me, the PM, and the room). So, until I calibrate, the offset is whatever it was when I calibrated during the last workout, which is likely innacurate for the correct workout, and I was just curious how the values displayed during the current workout prior to calibrating are affected, given the difference between the previous offset and the new/accurate offset obtained when I calibrate after the warmup.
If I understand correctly then, the offset measures the residual strain on the gauge with no external forces (feet not clipped in). Therefore the post-warmup offset of 12 is saying there are 12 units (I use the arbitrary “units” instead of watts since it’s not clear whether it actually represents watts) of force inherent in the gauge, so it needs to adjust for that by subtracting those units from the power numbers while I’m pedaling. But prior to calibrating, it was only subtracting 7 units of force, resulting in reporting power numbers that were greater than actual.
Let me know if I have anything wrong.