Could I benefit from using also the measurements of acceleration on y and z axes in some way? Should I change the acceleration range (currently it's set to 4G)? Up to which point is the temporal synchronization of the measurement on the two sensors important ? Should I smooth the data on time using median/lowpass filter before comparing ?????
a. I don't think so.
b. Range has to be correlated to max acceleration, there must not be a "clipping". Can you dump a data to buffer or PC, to verify clipping issue?
c. Obviously data has to be synchronous.
d. All depends on temporal scale : how fast do you need update rate ? 1 / 100 / 1000 per second?
How you sample a data, can you be sure freq. rate is exact? Filtering doesn't make sense w/o strictly defined two conditions.