My goal is to tune the piano so it sounds clean and clear in all ranges and stays in tune through the most vigorous playing. My experience with performance pianos has given me the chance to study my own work, to evaluate the instruments before and after the concert and to learn from artist's evaluations and self-criticism.
I tune by ear, most often using the 8:1 "triple" octave as a standard for stretch. In most pianos, when the 4:1 double octave is in tune, due to inharmonicity, the 8:1triple octave will be flat. I prefer to stretch the double octave slightly and have a pure triple octave. In this tuning style, the single octaves in the middle of the piano will be tuned pure at the 6:3 or 4:2 level, the double octave pure at 8:2 (usually 2 beats per second at 4:1) and the triple octave pure at 8:1.
The most frequently asked question I hear is "which is better, piano tuning by ear or with a machine?" My answer is, "The tuning is no better than the tuner." Good tuners, who have done their homework, who have tuned thousands of pianos, and who are their own worst critics, can do a nice job for you, regardless of whether they use an electronic device. If their piano tuning is not good, it's because they don't know how to tune or they didn't do a careful job, not because electronic piano tuning is inferior.
I tune by ear because I enjoy it, and because it keeps my ear trained. Because I tune by ear, I can choose by listening the stretch I want for a given piano. And because I tune by ear, I'm always listening to the quality of sound coming from the instrument, which helps when it's time to evaluate and improve its voice.
Piano Tuning Stability:
A stable piano tuning with clean unisons is most difficult to achieve. Piano tuning is hard work and it requires determination to stick with it until each unison is locked in. Laziness is a piano tuners worst enemy. If a piano is not tuned well, you can hear it straight away.
Stability is the result of using proper technique, having a strategy for changing the overall pitch of the instrument, and reviewing and refining the job. A piano tuner learns by using powerful "test blows" to see if a certain string will stay put. Over time we learn to recognize what an unstable pin feels like, and we compensate by stretching or retuning. The bottom line is whether the tuning is clean and solid and can withstand forceful playing when we are finished with it.
All pianos in the Northern Hemisphere go flat when the weather turns cold and the inside air dries out. They all go sharp in the humid summertime.
Loose tuning pins can make a piano untunable. If the pins are loose in the pin block, it's time to repair the instrument.