The piano is primarily made out of wood and metal. Wood is quite sensitive to humidity changes, while metal is quite sensitive to temperature changes. These two factors combine to produce an inherent instability in the piano, despite it having the greatest tuning stability of all stringed instruments. In climates such as Omaha's, where there are frequent and large changes in both temperature and humidity, pianos tend to go out of tune more quickly. If a piano remains untuned for long periods of time (even if it hasn't been played), the piano may fall so far out of tune as to be unplayable. To avoid this, it is recommended that you have your piano tuned at least twice a year in order to maximize stability.