The precision in which every piece must be calibrated to keep it functioning is very important for the pianist to be able to control the sound of his instrument from the loudest scale to the sweetest chord.

Every single part of the action is also made of wood, felt, leather and metal, thus being equally affected by humidity and temperature changes. They are also affected by many other things, such as moving the piano or just material weariness because of the use.

Every once in a while the action needs to be regulated to cope with these changes and let the pianist control the instrument at its best.

On the other hand, the piano also needs to be voiced every once in a while: Also because of material weariness, when the felt on the hammers gets either compacted or deformed it will change the tone of the note that is played. Commonly, that change is uneven amongst the hammers of the same piano, so a periodical work of voicing is needed for that to be fixed.

For more information on this subject, check the PTG technical bulletin on voicing.