There are three preferences for GravMag:
The Significant Digits to Display outside user-entered areas can be set. This is mainly of interest for seeing the calculated values in the Data Windows (especially when using full field values for magnetic anomalies).
Use Uncertainties on Data will allow entry of errors in the Data Windows and any uncertainties entered will be displayed on the Section Window.
When Enter Magnetic Field Directly is chosen, the orientation and direction of the Earth's field in the survey area can be entered into the Model Window. Otherwise the program will approximate the field with a dipole field centered on the true north pole.