Originally posted by LikeASong:What is the strobe tune, Jeff?
Strobe tuners are pretty much the most accurate tuners out there. Highly sensitive and highly accurate.
Dallas uses a few different Peterson Strobe tuners to keep The Edge in tune. In the October Music Radar Online article, it mentions:
Peterson V-Sam Tuner - Sells for $249.00 (Seems some online retailers are no longer carrying it. This might be that a newer version is forthcoming)
http://www.petersontuners.com/index.cfm?category=92
Peterson VS-F Strobo Flip - Sells for $199.00
http://www.petersontuners.com/index.cfm?category=37&sub=21

Peterson VS-R Strobo Rack Tuner - Sells for $359.00
http://www.petersontuners.com/index.cfm?category=73&sub=66

I remember seeing a picture from behind The Edge's amps, when they played at the Brooklyn Bridge, and there was a Peterson StroboStomp pedal (I have one and I swear by it - fantastic tuner!)

Here's a good wiki link that explains how a strobe tuners (and other tuners) work:
http://en.wikipedia.org/wiki/Electronic_tuner
The TC Electronic Polytune has a strobe tuning function. It is also pretty accurate. The Polytune is another tuner that is fantastic and one that is essential to me. And for the price, you can't beat it.

TC Electronics Polytune sells for $99.99
Peterson StroboStomp 2 sells for $199.00