Didger 4
Didger 4 will by default export GeoTIFF files in the Display Units. Go to File | Project Settings. On the General tab, check Export in Display Coordinates to export in the Display Units (checked by default) or uncheck this check box to revert to the old behavior of always exporting projected projects in meters. As with Didger 3, the only exception is Lat/Long. If your display units are Lat/Long, then Didger will still export the GeoTIFF in meters.

You can change the Display Units in Didger 4 by selecting the units from the drop down menu at the bottom of the Coordinate Manager (suggested method), or by going to View | Change Projection.

Didger 3
When Didger 3 (or Didger 2) exports a projected project to a GeoTIFF file, Didger will (by default) export it in units of meters.

The ability to export to GeoTIFF files in the Display Units was included in Didger version 3.06 (released March, 2004). If you are using Didger 3, make sure you are using Didger 3.06 or a later version (Help | About Didger). Then navigate to the Didger installation folder on your computer and open the Didger.ini file in a text editor, like Notepad. Under the [Settings] section at the top, change the Export Display line from 0 to 1, so that it looks like: