Robert,
You may choose either e- or DN units for the measurements Median, MeanDeviation, and Noise by selecting System Parameters > Data unit. If you choose e- units, you must also set a value for System Parameters > Camera gain. On the other hand, if you choose DN units, then the value of System Parameters > Camera gain is not used by the script.
If you do choose e- units, then use whatever gain value you think best characterizes your detector. If you are not sure, then just use DN units. The selected unit will appear in the Table, Plots, and Expressions sections of the script.
Thanks,
Mike