I don't understand something:
How do you get 1/2 tooth as a reading you're off by?

You rotate the ENGINE (counterclockwise) until the cam is showing to be lined up correctly, then you read the degree stretch on the crank hub. Is it off by 10°? That'd be 1/2 of a tooth, but 10° is a more accurate measurement. You CANT move the cam until it shows TDC, then check the engine. It will never show correctly, and the reading is typically not consistent either. You also can't move the cam close, then move the engine to TDC to finish it. You must move the engine by the crank soley to do this check.

If you're off by less than 10°, it's possible you have an offset tooth in that cam (put in by a previous mechanic)