#1
Hey guys,
While my first set of guitar lessons has ended so we're taking a break over summer meaning my guitar teacher is gone. Unfortunately he moved away which really sucks but has nothing to do with this...
Anyway, he used to always be the one to check out the intonation on my guitar and set it up right. He did this thing where he looked down the neck and made any adjustments from there and I was wondering if any of you guys could explain how you do this? I realise now I should've just asked him but it's too late so any help would be appreciated.
#2
It's absolutely impossible to sight down the neck of any guitar and adjust intonation based on that. Completely, 100% verifiably impossible. Intonation involves comparing the notes of each string at the open position to the fretted 12th position and adjusting individual scale length based on that. More than likely what he was doing was guessing at the fretboard relief and tweaking the truss rod accordingly. Also bad practice. Doesn't sound like any instructor I'd want.
#3
You may not have realized that he may have played the harmonic on the 12th fret to compare to the pitch of the the open string tone. That's how you can tell (without using a strobe tuner) if the if the string's intonation is correct. If pitch of the harmonic doesn't match the pitch of the open string tone, the bridge saddle must be adjusted forward or back accordingly until they do.

All of this assumes that if you physically measured from the nut to the center of the 12th fretwire, and then from the 12th fretwire to the bridge saddle that they would already be very close in measurement.
Jam On!