Interpreting ASensor accelerometer data


I am currently working on an app that needs to detect if a ASensor bumped.
I can read the accelerometers data from the advertising packet respectively on bytes 20 21 22.

I have installed your android demo app to read theses values

The issue I have now is that the acceleration data sometimes return 255 for acceleration X and Y when the sensor is not moving and acceleration Z is outputting the value of 63.

Is it something normal, should I consider 255 to be 0? What does this 63 constant value mean?

Is the ASensor sensitivity enough to detect a bump?

Thank you,