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A variometer is an instrument used in airplanes for indicating the climb and sink rate. The unit displayed is usually feet per minute (ft/min). In gliders in Germany, where SI units are used, variometers disply in meters per second (m/s). Some variometers display in knots (nautical miles per hour).

Variometers are vitally important in the sport of gliding, because human perception has no sense of climb and sink rates. Some people claim to be able to fly gliders without this instrument; however, humans only perceive changing accelerations due to changes in the climb/sink rate, with no way of telling the actual rate.

Diving a sailplane and pulling up a sailplane result in large changes in the climb and sink rate and in the aircraft velocity while exchanging kinetic energy for potential energy. Variometers can be compensated by using pressure differentials and much tubing (will explain this at a later time), so that only the net energy gain or loss is displayed. The effect of changing aircraft velocity can thus be eliminated, which is vital for a usable variometer display in gliders. In modern gliders, electronic variometers generate a sound depending on the instrument reading, improving flight safety by being something that can be called a heads-up display.

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