It is often thought that the piano tuner at work on a fine tuning, is listening to the pitches of the strings and adjusting the pitch of each string. In fact, in fine tuning, pitch plays a relatively small part in what the piano tuner is doing. In fine tuning, the piano tuner is primarily involved in adjusting tone, although it is true that pitch and tone are related.

Having the faculty of so-called "perfect pitch" or "absolute pitch" does not help in making the tone adjustments necessary in fine tuning a piano.

'Pitch' is not a precise, scientific measurable. It refers to a subjective perception, and the necessary scientific measurable is not pitch, but frequency. Frequency is a precise, objective measure of a number of cycles or vibrations per second. There is no SI scientific unit of pitch. 

Pitch perception is dependent on physiological and psychological factors. There is no established evidence that persons with "absolute" pitch (aka "perfect pitch") are able, as a result of having "absolute pitch", to detect pitch differences any smaller than persons without "absolute pitch". "Absolute pitch" is a different kind of ability.

Expert piano tuners using techniques of listening to tone, acquired through training and experience, are necessarily working with fine tone differences that correspond to frequency ratio changes of around one third of a cent (1/300th of a semitone, or 0.08Hz at A440) as a matter of normal everyday practice, and many fine tuners will work well inside this range when tuning unison string groups or octaves. These small differences are not significant to the musician's pitch perception in the context of all the other factors that are important in piano tone. They are, however, significant in tuning, because of their effect on tone.

Inside the limits of any pitch differences that the musician would notice in piano tones and intervals, the piano tuner constantly works with tone differences These have been "traditionally" described in a very limited way, in terms of a feature called beating in the soundscape. But even the "traditionally" documented understanding of beating, is a somewhat crude and generic simplification of the actual complex phenomena that takes place in the soundscape, that contributes to tone, and that the piano tuner has the opportunity to adjust.

As far as theory is concerned, the acoustics of beat phenomena and its relation to perceived tone is much more complex than "traditional" piano tuning theory suggests. Beat phenomena is also part of a broader psycho-acoustic dimension of tone perception. As far as practice is concerned, every master tuner already knows this from experience, and from direct empirical knowledge of piano tone. In "traditional" piano tuning theory there is no description at all of how master tuners actually create tone, but master tuners themselves are well aware that they do it, and that as in any art, the individual result is a hallmark of the individual tuner.