An indication for correct measurement is a relatively short measuring time of one to two seconds. The Truma LevelCheck then receives a clear signal and the display for the filled range (= green) or empty range (= red) is close to reliable.
A longer measuring time of three to ten seconds indicates an unclear signal and is acknowledged with a red display (= incorrect measurement).
If you measure a full gas cylinder near the bottom, you may get an incorrect measurement. This is due to the limited reflection of the echo at the distant surface of the LPG.