What is Piano Tuning?

The meaning of the term in tune in the context of piano tuning is not as straightforward as it might seem, as it does not refer to the assignment of particular fixed set of pitches as it may with other instruments. Fine piano tuning requires an assessment of the interaction between 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. In all systems of tuning, every pitch may be derived from its relationship to a chosen fixed pitch. In the case of piano tuning, A440 is the usual standard.

Piano tuning is distinct from repairs or other maintenance that may be carried out (e.g. regulation of the action). There are typically about 220 strings in a full-sized piano, which may have a combined tension of about 20 tonnes. Tuning involves making minute adjustments to the tensions of these strings, in order to properly align the intervals between their tones.
Temperament and beating

The relationship between two pitches, called an interval, is the ratio of their absolute frequencies. Two different intervals are perceived to be the same when the pairs of pitches involved share the same frequency ratio. The easiest intervals to identify, and the easiest intervals to tune, are those that are justâ€" which have a simple whole-number ratio. The term temperament refers to a tuning system which tempers the just intervals (usually the perfect fifth which has the ratio 3:2) in order to satisfy some other mathematical property; in equal temperament, to temper a fifth one slightly narrows it by flattening its upper pitch slightly, or raising its lower pitch slightly. A system of temperament can also be known as a set of bearings, a term derived from early treatises on temperament which asserted that a fifth could be flattened "as much as it can bear".