To regulate a piano is to adjust all of the parts so that they operate uniformly and efficiently. The greatest difference between a new and a used piano is that the parts in the used piano have become worn and no adjustments have been made to compensate for the wear.
To return your piano to its once perfect working order and restoring it’s touch and sound to optimal consistency involves adjusting different screws, replacing pins, or sanding wooden surfaces. This usually includes one or more of the following adjustments:
blow distance
key level and dip
lost motion
let-off
drop
hammer aligment
damper take-off
and more…