Peak to peak
rms doesn't make a whole lot of sense I guess. 
 They are mutually
exclusive...either you're measuring the peak value
 or the RMS value.  They are different. 
 
Actually, the peak value equals the RMS value for certain waveforms.
It's even possible for the peak-to-peak value to equal the RMS value,
but - I think! - not for waveforms that cross through zero.
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