Piano tuning
is the act of making minute adjustments to the tensions of the strings of a
piano to properly align the intervals between their tones so that the
instrument is in tune . The meaning of the term in tune in the context of
piano tuning is not simply a particular fixed set of pitches . Fine piano
tuning requires an assessment of the interaction among notes, which is
different for every piano, thus in practice requiring slightly different
pitches from any theoretical standard. Pianos are usually tuned to a modified
version of the system called equal temperament ( see Piano key frequencies for
the theoretical piano tuning ). In all systems of tuning, every pitch may be
derived from its relationship to a chosen fixed pitch, which is usually A440 .