Why does the piano tuner seem to pound the keys so hard?
Giving the key a firm “test blow” is an important step towards settling the string and thus allowing better tuning stability. The tuner strikes the key with sufficient force to better equalize the string tension across the few bearing points of the string’s length. Combine this pounding with proper tuning lever technique, and the piano will hold on to it’s tune. If the test blows are omitted, the first player to apply much force to the keys could knock the piano out of tune.
