All aircraft, including sailplanes, employ various instruments to determine specific flight characteristics. A pitot-static system is a set ofof pressure-sensitive instruments primarily utilised in aviation to determine an aircraft’s airspeed, altitude and altitude trend. A typical pitot-static system consists of a pitot tube, a static port and the pitot-static instruments.

A variometer is directly linked to the atmosphere via a total energy probe. The design of the total energy probe allows it to compensate for changes that do not involve the detection of rising and sinking air. The probe is typically positioned away from the aircraft to ensure measurements are taken in the free stream air, unaffected by the presence of flying surfaces. The pilot can determine the strength and stability of a thermal by observing the movement of the variometer indicator (Brandes, 1975; FAA, 2013; Nicks, 1976; Reid, 2009a).

For this reason, it is crucial that both the pitot-static and total energy instruments are of high and reliable quality, with precise manufacturing tolerances to ensure their accuracy.