The listerCompass allows a field geologist to take advantage of the iPhone's capabilities.
This is a professional compass designed by an expert structural geologist, used in the field to see what is practical and what is not.
You can measure surfaces and lineations at the same time. Orient the compass on the surface with the edge parallel to the lineation. If you only care about surfaces, the only thing to do is to place the compass parallel to the surface (any way you like).
Once it stabilizes, tap the screen. Double tap to record the data.
Data is collected, averaged, and presented in standard formats.