There are many moving parts inside your piano. Over 6000 pieces in fact! The performance and touch of your keys depend on how these parts are set. Overtime wooden parts warp, felts become flat, and felt on your Hammer disappears. These small changes add up to a big difference in your pianos performance. Out of Regulation enough, and keys will stop playing.
Regulation includes setting key height, reshaping hammers, repairs, pedal adjustment, and the list goes on and on. If your piano is nearing a hundred years old it most likely needs a lot of regulation with some repair. After doing so, your piano will play like it did when it was new! If you noticed that some keys don't play when you try to play softly, or it sounds like it is hitting a string twice, you need regulation.
Unequally spaced Keys, thumping noises from the pedal and keys with slow repetition are all due to your piano being out of regulation. Whether your piano is 20 years old or a hundred years old it needs regulation in order to play as good as it can.
Basic regulation includes only the repair and maintenance needed to bring regulation to an acceptable level. Upright 450 Grand 800
Fine regulation includes repairs necessary to bring action and keys to a like-new state. Upright 600 Grand 900