I formally studied under a Master Technician prior to the use of electronic tuning instruments. I was taught to use a tuning fork and to tune by ear in harmonics.
I learned voicing and regulation and action repair. That initial training plus some forty years of experience probably accounts for my being formally noted as:
Servicing major brands including Steinway, Yamaha, Kawai
Piano Tuner Dallas, Richardson, Park Cities, Mesquite, Garland, Rowlett and North Dallas