The ranges are labelled volts per div… so the 50 mv range is 50 mv per division. You would want to calibrate at mid scale or above. So perhaps 3 to 5 division would be mid scale. In this case use 3 to 5 times 50 mv; i.e. use 150-250mv. This is just a general rule. Hope it helps you.
The latest APP v2.45b displays recommended values for each scale as you move from one scale to another during the calibration process. Those recommended values tend to be around 5 to 6 x the volts per division for that scale.
My calibration results were less than satisfactory. Apparently the APP interpolation algorithm needs improvement.
And, by the way, the first post above is outdated. The APP v2.45b automatically calibrates the zero voltages. The cursor cannot be moved into the diff field. Instead you adjust the displayed voltage in the voltage field.
Paul