PiaTune uses an F3 - A4 temperament. Just like an aural tuner would do, first four contiguous M3rds are established between F3 and A4. Then the width of the fourths are optimized to get an even progression on major thirds, fourths and major sixths. Result is a perfect equal temperament.
The bass and treble is expanded from this temperament just like an aural tuner would do. PiaTune listens to the note and calculates the frequency that would satisfy the interval widths with the previously tuned notes.
Actual beat rates of major third, sixth and tenth intervals related to the temperament can be measured. Intervals range from G#2 to F4. The beat rates of fourths, fifths and 4:2 octaves within the temperament can be calculated using the measured values.
The first time you tune a piano the above described procedure is used. When you finish the tuning (or during the tuning) you can save the data. The next time you tune the same piano, it is as easy to load the previously saved file and tune the piano. This time, since all the targets are already calculated, you can tune the piano in any order you want. Even if you change the octave sizes, there is no limitation or pattern, because the calculations are done on the fly. You can also set auto save to automatically save current tuning every 5 minutes.
You can set A4 frequency to a value other than the standard pitch of 440 Hz. The frequency can be set between 392.00 Hz and 466.99 Hz with 0.01 Hz steps. You can also calibrate the A4 frequency of your device to a known source.
When the setting of the temperament is finished or you tune a previously tuned piano by loading the saved tuning file it is possible to change notes automatically. When AutoNote feature is active, if the note you played is in the range of plus/minus three semitones from the current note, PiaTune automatically switches to that note.
Depending on the size and scale of the piano you can choose different stretches. For the temperament octave and midrange you can choose a 4:2 octave, a compromise between a 4:2 octave and 6:3 octave or between a 2:1 octave and 4:2 octave. For the bass, 6:3, 8:4 and 10:5 octave sizes are available. For the treble a 4:1 octave size might be suitable for most pianos. But in case you prefer the last octave to be single octaves you can choose 2:1 octaves. For a wider stretch in high treble you can select 4:2 octaves.
There is also a special stretch for small pianos like spinets which will tune the bass section all 6:3 octaves.
Custom Offsets :
Offsets for A0, A1, A2, A3, A5, A6 and A7 can be entered directly or set by measuring these notes. PiaTune will generate a custom tuning curve according to these values instead of using Bass/Mid/Treble octave stretches.
Besides the default Equal Temperament, PiaTune comes loaded with a select number of unequal temperaments. The provided temperaments are, 1/3 Meantone, 1/4 Meantone, 1/5 Meantone, 1/6 Meantone, 2/7 Meantone, D’Alembert Well, Just, Kirnberger-III, Mersenne, Neidhardt 1, Neidhardt 1732, Pythagorean, Rameau, Valotti, Werckmeister-III, Young1 and Young2. You can add other unequal temperaments though the Temperament screen. Just enter the cent offsets of your temperament with A at zero offset. Also it is possible to transpose the temperament to other notes than the default note C.
When you activate the Overpull feature, the note frequency is briefly measured and an over pull value is calculated based on the over pull percentages you have set and the note being tuned. There are three over pull percentages that can be set, bass, midrange and treble.