Airspeed indicator

The airspeed indicator (ASI) or airspeed gauge is a flight instrument indicating the airspeed of an aircraft in kilometres per hour (km/h), knots (kn or kt), miles per hour (MPH) and/or metres per second (m/s). The recommendation by ICAO is to use km/h, however knots (kt) is currently the most used unit. The ASI measures the pressure differential between static pressure from the static port, and total pressure from the pitot tube. This difference in pressure is registered with the ASI pointer on the face of the instrument.^[1]

Single-engine ASI (left) with V speeds labelled, and Multi-engine ASI (centre) with blue and red radial lines, as well as (right) showing knots only