Chapter 6 MATH and Measurements    RIGOL 
DS2000E User’s Guide    6-25 
Press Vtop to select "Histogram" or "Vmax".   
―  Histogram: takes the voltage between the flat top of the waveform and 
the GND as the top value.  
―  Vmax: takes the maximum value of the waveform data as the top 
value. 
Press Vbase to select "Histogram" or "Vmin". 
―  Histogram: takes the voltage between the flat base of the waveform 
and the GND as the base value. 
―  Vmin: takes the minimum value of the waveform data as the base 
value.