Either way, your estimate can be out by quite a lot if you just compare the power meter with and without A/C. If the power meter reads "1kW" without and "2kW" with A/C, you'd assume that the A/C was consuming 1kW. But:Regardless of truncation or rounding, in average it should not matter as it happens both with and without A/C?
- with rounding the actual values might be anywhere from 0.8 and 2.5 (1.7 actual kW) to 1.5 and 1.6 (0.1 actual kW)
- with truncation it could be anywhere from 1.0 and 2.9, (1.9 actual kW) to 1.9 and 2.0 (0.1 actual kW)
So the power meter's lack of resolution really limits how accurately you can estimate things like this. That's why going to the kWh consumed display in the energy info screen can give you a much more accurate picture of what's going on.