Intonation
Whether a guitar plays in tune with itself all the way up the neck, not just on the open strings.
Why it matters
A guitar can be perfectly tuned open and still sound off higher up the neck if intonation isn't set correctly.
Used in a sentence
Digging deeper
Your open strings can be perfectly in tune while chords further up the neck still sound sour. That is intonation — whether fretted notes stay in tune with the open ones — and it is corrected by moving each string's saddle, not by tuning.
Common questions
How do I check my intonation?
Tune the open string, then compare the harmonic at the 12th fret with the note fretted at the 12th. If the fretted note reads sharp or flat against the harmonic, the intonation needs adjusting.
Can I fix bad intonation by tuning more carefully?
No. Tuning shifts every note on that string together, so it cannot fix a mismatch between open and fretted notes. That is a saddle adjustment — a setup job.
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