My 230 VAC looks like image attached. It’s not so much “unstable” in the common sense, since it’s always within tolerance and there are no power problems at all - but it does fluctuate a lot around 230V, making calibration pretty hard.
I’ll need to reflash the EmonTX to be able to add a NodeMCU clone running EmonESP. I stored a voltage calibration value in the currently running FW that is now lost, and I’m not completely sure it was right anyway. So I want to recalibrate it. What are the recommendations? I do have a true RMS DMM with adequate accuracy, but it’s next to impossible syncing the serial readings and the readings of the DMM. Should I try recording the DMM measurements for a few minutes somehow, calculate an average, do the same with the EmonTX serial output and calculate the ratio? Something else I can think of is generating stable 230VAC somehow. I have 2 UPS devices with “modified sine wave” output - could they be useful for this purpose? Any other ideas?