In early hang gliding, variometers were not needed for the short flights or flights close to ridge lift. But the variometer became key as pilots began making longer flights. The first portable variometer for use in hang gliders was the Colver Variometer, introduced in the 1970s by Colver Soaring Instruments,[11] which served to extend the sport into cross-country thermal flying.[12][13] In the 1980s, Ball Variometers Inc., founded in 1971 by Richard Harding Ball (1921–2011), produced a wrist variometer powered by a 9-volt battery.[14][15]