Originally Posted by
hamster
For static pressure you need a sensor that is on the outside of the unit. Garmin has a system of channels inside the mount that terminate at the intake port. There could be lines of flow that terminate inside the port. I guess it depends on the exact geometry.
It should be very easy to test. If Garmin normally measures stagnation pressure (as mounted on the bike), it has to do velocity correction. If it does velocity correction, it should immediately show up as a jump in elevation if you turn it on inside a car that accelerates from stand still to the freeway speed (you may need to crack rear windows to equalize pressure).
I've never seen a static pressure sensor on the outside of anything with one. From aircraft to model rockets to garmin head units, static pressure is measured via a port located perpendicular to the airflow and ducted to the sensor.
Stagnation pressure would be measured with a duct facing forward, and there is nothing like that on a garmin or it's mount. That sort of system would be wildly inaccurate with even the slightest breeze.