If I may add my two cents worth... I've used everything over the last 38 years from pitch pipes to electronic tuners but I've only ever found one way to consistently tune accurately and quickly and that is by ear. By that I mean one must actually practce tuning just like anything else you want to do well. Your ear must "know" the sound of 3rds 4ths and 5ths. This takes a little time but is well worth it. Then buy a good tuning fork tuned to A-440. Pluck the A string and while it rings, tap the tuning fork on your knee and place the butt end on your bridge. Comparing the open A tone to the tuning fork you will be able to set the "beat" to zero very quickly without the error inherent in using harmonics. Then play the A and bass E strings together and do the same thing. Follow this with the A and trebble E played together. Play the A and D together to tune the D, and the D and G together to tune the D. Finally, play the trebble E with the B string to tune the B. All strings are played open, no harmonics or fretted strings.

If the guitar is correctly set up, this will overcome the common error that occurs between the G and B strings. The whole guitar should fall naturally into perfect tune. In a noisey room, I hold my left ear on the side of the guitar as I tune. Makes everything loud enough to hear easily. I've come late to jam sessions and tuned this way in a corner while the group played. When I joined the group they wanted me to retune to their electronic tuner. I quickly ran through the strings in front of the gadget and it showed each string was exactly in tune. I maintain mine was the only instrument there that was completely in tune.

If you play an electric guitar this still works great. With your amp on, hold the vibrating tuning fork tines near one of your pickup poles and play the open A string as above. The electronics make the "beat" even easier to hear clearly.

This method pleases the ear, not necessarily the physicist which, after all, is what you want. It's fast, cheap, and you don't have to carry batteries. Even if your bridge is slightly off, you'll be in tune for most first position chords.

I don't have a great ear so I figure if I can learn to tune this way then most people probably already use it. On the other hand, I've run into very few people who do.

Hope this is useful to someone,

- Mark