Understanding accelerometer data

[rixed at happyleptic.org]

> yes. acceleration is change of velocity. if there is no change in
> velocity, there will be no acceleration. hence, if the phone is still,
> all acc values should be zero. gravity or not, there is no net acc on
> the phone. i don't know the format the accelerometers output data in,
> but i'd take a punt that the values shown are noise.

No. Accelerometers do not measure change in velocity, but change in
velocity + gravity.

There is no way to build an engine that would distinguish change in
velocity from gravity (lookup equivalence gravity/acceleration in
wikipedia for some interresting reading).

Thus, what you have here is noise added to gravity in the vertical
direction.

Kindly,