Every note on a grand piano has more than 35 points of adjustment. Every note on a vertical action has over 25 points of adjustment. As a conscientious piano owner, you probably have your piano tuned regularly by a qualified technician. You may, however, notice a deterioration of its performance despite regular tuning. It's important to note that tuning is only the adjustment of the system of strings and pins that determines the pitch of each string. Your piano also requires a periodic servicing called regulation, which attends to the mechanical parts which cause strings to sound when keys are played and affect the sound through use of the pedals.
Regulation is the adjustment of the mechanical aspects of the piano to compensate for the effects of wear, the compacting and settling of cloth, felt and buckskin, as well as dimensional changes in wood and wool parts due to changes in humidity.
The three systems involved in regulation are the action, trap work and damper system. The action is the mechanical part of the piano that transfers the motion of the fingers on the keys to the hammers that strike the strings. It is comprised of over 9,000 parts which require adjustment to critical tolerances to be able to respond to the pianist's every command. The trap work is the assemblage of levers, dowels and springs that connects the pedals to the action affecting sustain and dynamics. The damper system is the mechanical part of the piano that stops the vibration of the string when you release the key and is controlled by the key and pedal systems.
All upright and grand pianos need periodic regulation to perform their best. Frequency of regulation is dependent upon amount of use, exposure to climatic changes, and the instrument's quality, age and condition. New pianos may require regulation in their first year because settling and compacting of parts sometime necessitates adjustment.
If your instrument displays a lack of sensitivity or a decreased dynamic range, it's a candidate for regulation. If you notice that the keys are not level, the touch is uneven or that the keys are sticking, the need for regulation is indicated.