Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Unless the voltmeter is specifically stated to be true RMS responding, then it responds to the average value of the waveform but is calibrated to display the RMS value of a sine-wave (1.1 times the average measurement). Thus for any waveform other than a sine-wave it will be in error, the amount of error depending upon how much difference there is between it's average and RMS values as compared to a sine-wave.