im trying to set up the inotation, im using a tunner

so i pick the string while presing on the 12 fret.. its to sharp
i then pick it again and its perfect intune
then i pick it again and its to sharp onece again
so i decide to play a harmonic on the 12th fret, its all good
but then i pick the string while pressing on the 12th fret. and its two sharp

whats happening??
make sure you are putting the same amount of pressure on the string each time; the harder you push, the sharper it will read. put about as much as you normally would while playing, and make sure you are fretting close to the fret.

from what i have heard, using the 12th fret to fix your intonation is less reliable than using, say, the 17th (havent tried it though, and it might be hard with some tuners).

personally, i don't see the fuss if its just a tad sharp/flat since you aren't always going to be able to put the exact same ammount of pressure on the string every time while playing.
Intonation Setup have a look there.

Also you check at the 12th fret because it is, when properly intonated, one octave above the open string.
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