![Taiwan, Province of China[a]](https://files.upgates.com/graphics/countries/tw.svg "Taiwan, Province of China[a]"){kind=small}
These true speed indicators are differential pressure indicators that measure the difference between static and total pressure produced by ram air from the pitot. The indicated airspeed can be corrected for changes in altitude by turning the knob to align the outside air temperature with the altitude. The moveable airspeed scale will then show the actual, or true, airspeed.
Sigma-Tek
