About 90% of an acoustic piano is made of wood. The wooden frame is reinforced with a cast iron ‘plate’ in order to withstand almost 20 tons of torque. Changes in temperature and humidity will directly affect the tuning stability of a piano.
When wood swells or contracts with the change of seasons, the tension on the 250 strings in a piano, changes also. String tension must be adjusted (tuned) to restore standard A-440 pitch.
A neglected piano may need more than one piano tuning to ‘stretch’ the stings and maintain pitch. It is always cheaper to maintain a piano than it is to restore a piano to pitch. The playing benefits of a well-tuned piano are enormous.