 Most pilots use variometers, radios, and, increasingly, GNSS units when they are flying.The main purpose of a variometer is in helping a pilot find and stay in the "core" of a thermal to maximise height gain and, conversely, to indicate when a pilot is in sinking air and needs to find rising air.Humans can sense the acceleration when they first hit a thermal, but cannot detect the difference between constant rising air and constant sinking air.