affect the tuning. If one holds a small metal flue pipe briefly in one's hand and then returns it to the chest, its pitch (relative to a tuning reference) can be heard to change as the pipe returns to room temperature. If two pipes of the same pitch stand close to each other on the chest, they can draw each other into tune, even though their pitches are slightly off when played individually. The pitch of very low-pitched pipes (in the 16′ and 32′ octaves) can be inaudible close to the pipe. Organ tuners often listen for beats between harmonics rather than the fundamentals. The audibility of these harmonics is extremely sensitive to the position of one's ears relative to the pipes. Eliminating the beats brings the pipe into tune. Humidity is a factor in maintaining wooden pipes. Many churches use humidifiers/dehumidifiers in an attempt to keep the organ loft from drying or becoming too moist. These devices must be carefully monitored and managed to avoid creating the opposite problem. In fact, controlling the climate around a pipe organ can have a significant impact on its tuning and maintenance schedule. For example, while many pipe organs require tuning or other maintenance more than once a year, the Marcussen pipe organ on the campus of Wichita State University in Kansas is carefully kept at 72 degrees Fahrenheit and 50% humidity year round and requires tuning and maintenance only once every four years. Its Danish caretakers credit meticulous climate control. References Pipe organ Musical tuning