At the risk of sounding like a braggart; I'll bet you I can walk up to any guitar in the guitar shop and tune it to perfect concert pitch by ear. I have lots of experience and a damn good ear. I can always tune my own instrument perfectly and can "sweeten" my tuning on the fly to approximate the jam session's relative tune (they are usually out a bit). I say all this because I firmly believe in the use of electronic tuners! Especially at sessions. They are the polite way for being sure that you will sound good with your neighbors. When instruments like harmonicas, whistles, some accordians, banjos - other instruments that may be less precise then a guitar are being played - it is most important that YOU are precise, to blend better. You can't do much to fix the harmonica or the whistle or the accordian - so your precision on the guitar is very important - if then you discover that the whole room is out a bit, but is relatively OK - you may want to "sweeten" your tuning to accommodate. But knowing what is precise tuning is the all important starting point. I vote for good ears AND electronic tuners!