Hello Alann,
The NI High-Speed Digitizers help is very useful in defining these types of terms.
From the help "Reference levels are high, low, and mid range values that you set to take rise time, fall time, width negative, width positive, duty cycle positive, and duty cycle negative measurements. Reference levels are generally configured in terms of the percentage of the waveform you acquire. By default, the low value is 10% of the waveform, the mid level is 50%, and the high value is 90%."
Also from the NI High-Speed Digitizers help "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 only relation between these two concepts is in the fact that the vertical range defines the maximum peak values of your input signal, which also restricts your high and low reference levels.
If you haven't installed the NI-Scope driver, but would still want to reference the help file it is available for download here.
