The apps on the cell phones work pretty well. They turn your phone into a angle meter and are zero resettable also. If you use the transom to set zero the numbers will always mean the same thing using that to reference off of. It doesn't matter what angle 0 is as long as you know where it likes and then you vary the trim up or down accordingly. It will also do tab angle if used with a straightedge.
Seen a lot of people with the little cube type of angle finder.