NO1 is average (not peak)
RMS is root mean square
Both are historical ways of measuring voltage in alternating current- like the electricity in your have in your house. VV/VW devices like the Vamo use pulse width modulation, which is similar to AC or alternating current.
RMS is generally considered the most accurate measurement.
One is not really expected to switch between one or the other.
There is no reason I can think of for any
device to use the AVG method, which is why NO1 was removed in the Vamo V3.