. . . You can easily get more high tech, expensive, fiddly solutions. But we have not seen the need.
Both the iPhone and Truma apps are free and simple to use.
If you already have a cell phone can't get any cheaper than free.
The iPhone compass app has a level function.
Level is now in the 'Measure' app on new iPhones.
Hasn't been a problem finding sites where 3" change is enough.
I would have missed some great boondocking sites if 3" was my limit.