Actaully there are many different temperaments. The most common ist of course the equal which you find in any standard tuner or you can make by ear on the 5th fret.

I mostly use this one too because it fits into most applications specially on rock you need to have perfect pitch for the powerchords otherwise they sound pretty blury.

I had a talk once with my piano tuner who also tunes piano's for the big concert halls in Zürich when people like Herbie Hancock are perfoming or at the conservatory and he told me that he uses a slight higher pitch on the high notes which makes the piano sound more brilliant. I tested this on the guitar by tuning the high stings a little bit higher and in fact I liked the effect.

On accoustic guitars it is also very tricky to tune it because the guitar as an instrument itself is not a perfect instrument. So if you are strict you always have to make compromises. If you tune in in perfect pitch it sounds perfect from till maximum the 5th fret - so my solution I choose is to tune the guitar in octaves in the 5th fret. This way you have the best compromise for the low and high positions and I play mostly aroung the 3-7 fret.

But as I said if you dont want to go so much in detail you just use standard tuning. If works fine for many applications.

HP