Vertical range is the peak-to-peak voltage span that a digitizer can measure at the input connector. Most digitizers have several choices for vertical range. The NI ELVIS III has two hardware-defined ranges, 2 Vpk-pk and 50 Vpk-pk.
Using this offset allows you to examine small changes in the input signal, which can improve the accuracy of your measurement. Set the vertical offset to match the nominal DC voltage and the signal appears centered on the screen.
Vertical offset does not influence all the parameter measurements such as the waveform amplitude, max value, or min value.
The vertical offset has a similar influence with the vertical position. The vertical position is a display function. Adjust the vertical position to place the waveforms where you want to see them. The waveform baseline locations track adjustments made to their positions.
Vertical offset is a little different as it includes hardware adjustment while vertical position is only a software function. The vertical offset voltage is applied after the oscilloscope preamplifier and can be used to increase the effective dynamic range of the inputs.