@palm369 You are correct about how the sensor works. But because we are not interested in a mass flow number, but a differential pressure number you do require an external barometer (which we of course have on the autopilot), but any errors with this will propagate to the airspeed driver. Further the sensor is designed to be used without tubing. When used with tubing you need to compensate for the pressure drop in the hose, which does scale with altitude (and temperature). https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/8_Differential_Pressure/Sensirion_Differential_Pressure_Sensors_SDP3x_Pressure_Drop_In_Hose.pdf