Notio supplies the app and the firmware for the Garmin Unit.
The software is Golden Cheetah
CdA is quite stable in the exact same setup considering that CdA is inherently erratic as power and speed are. For instance, if you start to oscillate in a headwind you CdA will get worst if you go smoothly with tailwind (sorry about my “Yoda style English “ )
For instance, these are 3 runs for a pro triathlete (same position, out and back constant power, out and back progressive power, and out and back in a Shrug position” [inline "Captura de pantalla 2018-07-10 a las 23.30.34.png"]