Sound is formed through complex wave interactions. As a piano’s materials naturally age and undergo changes such as oxidation, its tonal characteristics and overtones also evolve. Aural tuning responds to these changes by carefully listening to the instrument, allowing the tuner to optimise its sound based on its current condition—bringing out the best musical balance despite natural inharmonicity introduced over time.

Click here to read American Physicist Richard Feyman's letter to his piano tuner: "pay more attention to ear-created harmonics".

According to ISO 16:1975, the International Organization for Standardization sets the international concert pitch at A4 = 440 Hz. This standardization was welcomed after decades of variation across countries, orchestras, and even over time, which made it difficult for musicians with instruments built to different pitches to play together harmoniously. Most recorded music in the modern era is recorded to standardized pitch. 

The act of tuning is very much a technician's practice of applied physics. 

If the piano string has to be stretched/compressed a whole lot to get to A440hz, the tendency of the string going out of tune is much faster than a piano that was already at A440hz. Therefore, the tuner must conduct pitch raising to ensure the piano is stable at 440Hz before proper piano tuning can be conducted.

After much thought, I have decided it is a win-win situation to charge customers for the pitch raising service if it is +/-5hz from A440hz. Pitch raising can be abandoned at times when the piano can no longer be pitch-raised (e.g. too rusty), or the customer wants to opt out of the service.