This cutaway view of the piano action shows one key and its movement. When the front of the key is pressed down, the back comes up. It raises the underlever which lifts the damper of the string. At the same time, the capstan screw pushes the support up, which in turn flips the hammer so it strikes the string.

The action of the keys is tested to make sure the keys will respond evenly to the pianist's finger pressure. In the "weigh-off" process, a lead weight is placed on each key. A worker observes how far and how fast the key moves when the weight is applied, and makes any necessary adjustments until all eighty-eight keys respond exactly the same way. Then the action and the keyboard are put into the case. Then it's time for the damper man to install the dampers and damper guide rails into the piano.

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