Before revision: The first portable variometer for use in hang gliders was the Colver Variometer by Colver Soaring Instruments Colver Soaring Instruments in British Hang Gliding History which served to extend the sport into cross-country thermal flying.Frank Colver, Colver VariometerThe Origin and History of Colver and Roberts Variometers
After revision: , introduced in the 1970s,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.The first portable variometer for use in hang gliders was the Colver Variometer by Colver Soaring Instruments Colver Soaring Instruments in British Hang Gliding History which served to extend the sport into cross-country thermal flying.Frank Colver, Colver VariometerThe Origin and History of Colver and Roberts Variometers