The crest factor varies with the waveform. Thus a sinusoid has a crest factor of 1/√2, a triangle or sawtooth wave has a crest factor of 1/√3, and a square-wave has a crest factor of 1. It is typically used when specifying true RMS meters, as there is a limit to the value of crest factor that they can accurately measure. Generally the higher the crest factor they can accommodate, the better the meter.

What do manufacturers mean when they say crest factor of 2 at full scale and 4 at half scale?

 

What do manufacturers mean when they say crest factor of 2 at full scale and 4 at half scale?

It means that there is some internal circuitry that will clip at high crest factors (high peak voltage as compared to the RMS voltage), giving an incorrect voltage reading.
The clipping obviously would occur at a lower crest factor at a full-scale output reading, as compared to a half-scale output.

 

Google Don Lancaster who wrote some interesting articles referred to crest factor.

/EDIT
Is this a 2nd thread on the same subject?
EDIT/

 

It means that there is some internal circuitry that will clip at high crest factors (high peak voltage as compared to the RMS voltage), giving an incorrect voltage reading.
The clipping obviously would occur at a lower crest factor at a full-scale output reading, as compared to a half-scale output.

So in this case, if I'm in the 6.000 V range trying to measure something above 3 V the meter will only be able to accurately handle 1.5 crest factor signals. Correct?