Offset in z-axis and Wrong Tap Detection problem in ADXL345

Hi! This is my first post here.
I am working on a project which involves working on ADXL345 and Arduino UNO. ADXL345 is supposed to detect impacts in all directions.

I am using ADXL345 in 10-bit resolution with +/-16g range.

I have been facing a number of problems here :
1. Despite putting ADXL345 on a flat surface there is an offset in Axis - Z values.

2. MAJOR PROBLEM!!! : While I was doing some controlled testing to set a threshold, I put the value of TapThreshold as 170 (~5g). I...

Offset in z-axis and Wrong Tap Detection problem in ADXL345