App for Determining Plumbness of a Vertical Structure

I work with vertical steel most of the time (monopoles, self-support cell towers, sports lighting) and have been running into an issue with sports lighting poles recently.

We are trying to determine the plumbness of the poles without spending an entire day using survey equipment like a theodolite.

Does anybody know of an app that might allow me to determine a *pretty close ish* estimate of the degrees in which a structure is out of plumb?

Some methods (aside from the theodolite, which we do use sometimes) is just estimating using the horizon and a string with a plumb bob on the end of it or estimating using a level from a good distance away from the pole.