... and you also do not really need to. At least as long as you do not ask us how to set the incline on your treadmill. Your Garmin watch does not need to know the incline. If you are concerned about the reporting of burned calories, then those are estimated from your heart rate, avg. resting HR, max HR, HR Variability, from body parameters, etc.. (and on devices with the PulseOx sensor, also with the help of the built-in oximetry).
