What is pitch correction?
When a piano is tuned, first the tuner tunes one note, usually the A above middle C, to a standard such as a tuning fork or electronic signal. Typically, the standard is A vibrating at a frequency of 440 cycles per second. Then the rest of the piano is tuned relative to that pitch. When, because of neglect or humidity changes, the pitch standard note is no longer at the correct pitch, the standard pitch must be reestablished and the piano roughly tuned relative to that pitch. This is called pitch correction. After the pitch correction, a fine tuning can be done. If a fine tuning is attempted at the same time as a pitch correction, the piano will usually end up out of tune because the strings have a tendency to revert to their old tension when a large change in tension is attempted at one time.
