The term Variometer also refers to a type of tunable electrical transformer A variometer (also known as a rate-of-climb indicator, a vertical speed indicator (VSI), or a vertical velocity indicator (VVI)) is an instrument in an aircraft used to inform the pilot of the instantaneous rate of descent or climb. It can be calibrated in knots, feet per minute (101 ft/min simeq 1 kt) or metres per second, depending on country and type of aircraft. In powered flight the pilot makes frequent use of the V… (More on Variometer)