Variometer

The variometer(aka vario) indicates the rate of climb and descent of the glider in units called knots. One knot is equal to approximately 100 feet per minute.

The variometer operates on the same principle as the altimeter, however, it indicates rate of climb or descent instead of vertical distance. The variometer depends upon the pressure lapse rate in the atmosphere to derive information about rate of climb or rate of descent. 

The variometer pictured to the left is a mechanical vario. Electrically powered varios serve the same purpose but often include an audio output to that correlates to the strength of the lift that they are experiencing at the moment. The audio output is a beeping noise that varies in pitch and rate of beeping. High pitch and fast beeping correlates to strong lift(rate of ascent). These sounds allow the glider pilots to maintain a good visual scan outside of the cockpit for other nearby aircraft instead of looking at the instrument itself. Watch and listen to this video to hear an example of an audio vario.

Most Gliders have 'Total Energy Variometers'. More...