Rule 12: Check Intonation And Sustain.

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"The neck is great on my ES-335. It's connected perfectly. The intonation is so true, it sings like a bird. I can tune it and put it back in the case, and then, take it out a week later, even two weeks sometimes, and it's perfect."

Intonation is the ability of the guitar to maintain tune the entire length of the scale. Accurate intonation is critical to sound quality. There is a simple test for it, and the guitar doesn't even have to be in tune.

The twelfth fret of the fingerboard is the middle of the scale. Therefore - at that point - each string when played open or fretted should be the same note whether the string is in tune or not. If the instrument has good intonation, you will know it from this test.

Intonation can be adjusted with Gibson's Tune-o-matic bridge, and the adjustable truss rod inside the neck.

Sustain is affected by several factors. Compare several instruments. Play each string open, and listen for sustain. Feel for vibration. The headstock should vibrate as much as the body. If it doesn't, the problem can be the neck joint or the type of wood. Sustain is also adversely affected by pick-up magnets not being centered under the strings or even the depth of the notches cut into the nut.