Mapping A4
It all begins with A4. A4 is tuned to A440 which on a well calibrated SAT will be (A4 @ 0.0). So pick a string of A4, and tune it to stop the lights.
Piano Manufacturers recommendations for piano tuning
Steinway & Sons … Unfortunately, no matter how expertly a piano is tuned, atmospheric variations, particularly humidity, and the nature of the piano’s construction constantly conspire to bring it off pitch. Your Steinway piano has been designed and built so that in normal use and under normal conditions it should need only periodic tuning. We…
Registered Piano Technician (RPT)
The field of Piano technology is an unregulated trade. Therefore the Piano Technicians Guild has set its own standards of quality for piano technicians.