I bought a cheap Digital angle finder (£25) a while ago. I checked mine against a sine bar and it appears to be well within the 0.05 degree spec.

It's handy for setting tool grinding angles etc but is a bit big and awkward for use on the mill. Its biggest problem however, is it eats batteries (3v lithium cell) even while 'off' (since off just blanks the display).

I'm tempted to saw the box down to make it smaller and easier to use, and fit it a pair of AA cells with a proper power switch.

See inside one here: http://homepage.ntlworld.com/bill_todd/DAF/daf.html

Bill