I think my digital protractor is about 5-6" - that seemed to be size that was biggest but would still allow me to adjust the miter saw.
You can do a simple test on these for accuracy, if you're curious. Just put the 'closed' protractor on a piece of glass (or something else known flat), turn it on and make sure it reads '0.0' degrees. Then, open it fully to 180 degrees, again check it on the glass that it is perfectly flat, and see what the readout indicates. Mine is usually within .2 degrees.
In most cases, .2 degrees is going to be plenty accurate for woodworking. No tool is perfectly accurate, and I really like the convenience of a digital readout, as I do work with odd angles sometimes.
On accuracy vs. resolution: Keep in mind, that probably the accuracy of the tool at smaller angles is within .1 degree. Probably, the more you open/move the protractor, the less accurate it becomes. Really, they should quantify the accuracy better (as in, .2 degrees per 360 degrees movement, or .2 degrees per 180 movement.)
Last edited by pweller; 04-30-2016 at 05:02 PM.