Like I wrote above, this is due to Pythagore (I don't know the name in English, it might be Pythagorus) Who invented the formula to find the frets' spacing. He didn't think about the strings gauges, or the little imperfections of the strings. Buzz Feiten invented a way to sound in tune everywhere on the neck. I've heard it was amazing, Van Halen, VAI, Satch, jazz greats all use this system. Anyone owns a guitar with this system (high ends washburns have it, I've heard...)