Documentation and logic improvements, values corrected

Hello,

The documentation was referring to the wrong sensor so I corrected this.

I also found problems with the accelerometer and magnetometer readings.  Note how in the new serial output example below the Z axis now has a value of 0.96g (gravity) and the other axes are closer to zero.  The magnetometer readings are no longer displaying things like NaN and seem to be plausible values in my testing.  

Example:
```
**************
Acceleration of X,Y,Z is
0.10g
0.00g
0.96g
The clockwise angle between the magnetic north and x-axis: 
17.212 degrees
The clockwise angle between the magnetic north and the projection of the positive x-axis in the horizontal plane: 
14.343 degrees
**************
Acceleration of X,Y,Z is
0.11g
0.00g
0.95g
The clockwise angle between the magnetic north and x-axis: 
17.945 degrees
The clockwise angle between the magnetic north and the projection of the positive x-axis in the horizontal plane: 
15.262 degrees
**************
Acceleration of X,Y,Z is
0.08g
0.01g
0.94g
The clockwise angle between the magnetic north and x-axis: 
19.566 degrees
The clockwise angle between the magnetic north and the projection of the positive x-axis in the horizontal plane: 
17.346 degrees
**************
```

Please consider merging these improvements.

Thank you,
Benjamin