Electronic Tuning vs Aural Tuning
Before beginning this page, I have to say it is necessary to tune a piano a minimum of once every year to maintain tuning stability. Some require more than once a year. Symphonies and recorder studios tune many times a year.
For more than three hundred years pianos have been tuned only with a tuning fork and an ear. In the 1980’s, reliable electronic tuning devices (known as ETD’s) were developed. I own two of them and often use them to do tonal measurements or pitch raises.
However, different brands and sizes of pianos have these different string scales. These are formulas created by the designer to develop the best tone based on string diameter and length.