The inner playing mechanism, called the “action” of a piano, is an amazingly complex and sensitive machine. Like any other machine, it needs to be kept in adjustment so that it works the way it was meant to work when it was built. Each key on your piano has more then 25 points of adjustment which need to work together to produce the sound you hear when you play just one note!
Regulation is the adjustment of the mechanical parts of the piano’s action optimizingits performance to compensate for the effects of wear and tear, the compacting and settling of cloth, felt, and leather, as well as dimensional changes in wood and felt parts due to changes in humidity and temperature. The three systems implicated in regulation are the action, pedal system and keyboard.