Tuned open but sour up the neck? That's intonation — and it's measurable. Pluck each string open, then at the 12th fret; the engine compares them in cents and tells you which saddles need a word.
Tune up first with the tuner — intonation numbers only mean something on a tuned instrument. Fret the 12th normally: squeezing hard bends it sharp and blames an innocent saddle.
A string in good intonation reads within ±3 cents at the 12th fret of where its open octave should be. Sharp at the 12th means the vibrating length is effectively too short — the saddle needs to move back, away from the neck. Flat means the opposite. Up to ±8 cents most ears forgive in chords; past that, barre chords up the neck start sounding seasick no matter how carefully you tune.
Two honest caveats. Old, dead strings intonate badly and no saddle can save them — restring before you measure, or at least distrust drama from strings older than a few months. And if you're not comfortable turning saddle screws, this report is exactly the thing to hand a guitar tech: it turns "something sounds off" into "the D string is 9 cents sharp at the 12th".