I got some levels like Dave/Satin Snow noted, but never bothered to install any.
For some reason, I carry around one of those carpenter's needle-indicator inclinometers. I just picked up a second one for $2.99 on sale at one of those Chinese-import 'disposable' tool stores.
I would NOT recommend their $20 imitation Dremel Tool on sale for $8. I figured before I used any of the rotary accessories I better wear two pairs of safety glasses, a hard hat & a baseball cup. They were honest with the speed rating...it said 16500 rpm, no load. That was true. Put a load on it and it stops :O). Might be able to clean a lens with it.