In aviation, a variometer – also known as a rate of climb and descent indicator (RCDI), rate-of-climb indicator, vertical speed indicator (VSI), or vertical velocity indicator (VVI) – is one of the flight instruments in an aircraft used to inform the pilot of the rate of descent or climb. It can be calibrated in metres per second, feet per minute or knots, depending on country and type of aircraft. It is typically connected to the aircraft's external static pressure source.
The vertical speed indicator from a Robinson R22. This is the most common type used in aircraft, showing vertical speed in feet per minute (ft/min).
Diaphragm Variometer operation
Schematic drawing of the internals of a classic aircraft vertical speed indicator
Panel mounted variometer for gliders, showing vertical speed in knots (kn).
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with data about the flight situation of that aircraft, such as altitude, airspeed, vertical speed, heading and much more other crucial information in flight. They improve safety by allowing the pilot to fly the aircraft in level flight, and make turns, without a reference outside the aircraft such as the horizon. Visual flight rules (VFR) require an airspeed indicator, an altimeter, and a compass or other suitable magnetic direction indicator. Instrument flight rules (IFR) additionally require a gyroscopic pitch-bank, direction and rate of turn indicator, plus a slip-skid indicator, adjustable altimeter, and a clock. Flight into instrument meteorological conditions (IMC) require radio navigation instruments for precise takeoffs and landings.
The cockpit of a Slingsby T-67 Firefly two-seat light airplane. The flight instruments are visible on the left of the instrument panel
Six basic instruments in a light twin-engine airplane arranged in a "basic-T". From top left: airspeed indicator, attitude indicator, altimeter, turn coordinator, heading indicator, and vertical speed indicator
Image: Aero Magnetic Compass