Intonation

Unlike a piano, a string instrument has no fixed pitches, which is a burden and an advantage. The burden is that every note must be placed and checked. The advantage is that a player can adjust, raising a leading tone toward its resolution, or tuning a third slightly low so a chord locks, in ways a fixed-pitch instrument cannot.

Practically, good intonation comes from feedback rather than effort: checking notes against open strings, listening for sympathetic resonance when a stopped note matches an open one, and using a tuner or drone to build a reliable internal reference. Cents are the unit of measurement, a hundred cents to a half step, with about five cents being the threshold where an average listener hears a note as out of tune.