best way to sharpen a chain saw?

For 35 years or so, I've found Granberg's file guide to be the simplest way to keep precise razor edges on LP-3/8" and std 38" chain. Minimal metal removal.
Very simple to set and hold angles, and set depth-gauges. Clamps on bar and separately clamps chain to avoid wobbling while filing.
Never had a chain that wouldn't cut straight, with nice BIG chips.
I've tried the electrically-powered grinders with the ~3/16" diam stones. No thanks.

That looks very good does it put the same angle as factory? I do not like doing it with a file because it does not seem to stay as sharp for me with a round file. I will have to check that out if it can put the factory angle on it.