Difference between True RMS and MEAN testers

QWhat is the difference between True RMS and MEAN testers?


In the field of electricity, AC signals are defined as RMS values.
There are two AC rectification methods for testers: True RMS and MEAN.
Both indicate the same value as long as there is no distortion in the  waveforms.
However, the two values will be different if there is distortion generated by inverters and/or switching power supplies.
True RMS testers measure the correct RMS value even if the waveform is distorted.