Why does piano go out of tune?
Pianos go out of tune mostly because of seasonal changes in humidity that cause the soundboard and other parts to alternately swell and shrink. This happens regardless of whether or not the piano is played. Pianos vary in their responsiveness to fluctuations in humidity, but the variance is not always related to the quality of the instrument. People also differ in their sensitivity to tuning changes.
New pianos should be tuned more often first year?
New or newly restored pianos should be tuned three or four times the first year, until the strings are fully stretched out. After that, most pianos should be tuned between one and three times per year, depending on seasonal humidity changes, the player's sensitivity, and the amount of use.
What is Concert Pitch A440?
Concert pitch A44(A above middle C vibrating at 440 times per second)has been universally accepted as the pitch to which all instruments should be tuned. It ensures that when instruments play together,they will all be in tune with one another.
Pianots are designed and built to sound therir best when tuned to A440. So when your piano's pitch drop's due to lack of tuning, the quality of tones suffers. Also, if piano is not tuned for quite some time, its pitch begins to slip far enough away from concert pitch that it may require a pitch raise in order to achieve a stable tuning.