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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
It should be identical. In fact if you try https://intel.github.io/generic-sensor-demos/sensor-info/build/bundled/ on your phone (choose + then accelerometer) you will see sensor values that include gravity too.
It's measuring gravity because that is an acceleration it is experiencing - if you were to throw it in the air then while it was in freefall you should see a proper 0 accelaration value.
If you want to try and remove the effect of gravity then for the car acceleration case I'd just take a reading when the user presses the 'start measuring' button and then subtract it from what you get next time.
However, actually getting a proper 0 value when the watch is on your arm is harder than it seems - realistically you need a gyro as well (which Bangle.js doesn't have) so the Bangle can keep track of what angle it is in in 3D space and then subtract the effect of gravity.