There are a number of designated airspeeds relating to optimum rates of ascent, the two most important of these are VX and VY.
At maximum weight it has a VY of 75 kn (139 km/h) indicated airspeed[4] providing a rate of climb of 721 ft/min (3.66 m/s).
[5] It can be calibrated in metres per second, feet per minute (1 ft/min = 0.00508 m/s) or knots (1 kn ≈ 0.514 m/s), depending on country and type of aircraft.
In gliding, the instrument is used almost continuously during normal flight, often with an audible output, to inform the pilot of rising or sinking air.
The instrument is of little interest during launching and landing, with the exception of aerotow, where the pilot will usually want to avoid releasing in sink.