Calibrating ADXL345 as per Sparkfun and Adafruit Guides - Calculations assist?

Hello,

I am trying to calibrate a ADXL345 accelerator using the sparkfun and adafruit guides as per:

https://learn.sparkfun.com/tutorials/adxl345-hookup-guide https://learn.adafruit.com/adxl345-digital-accelerometer/programming

I used both as 1 was better in one area, and the other in another area, but regardless I am not sure how I go from the result to the calculated offsets and gain to modify the raw data.

As per the sparkfun guide linked above:

Calculations

The offset values and gain factors are calculated with the following equations as stated in the Application Note from Analog Devices (page 8: equations 17 and 18).

In the DEFINED VARIABLES section of the code is where we will place the new calculated values for offset and gain.

/************** DEFINED VARIABLES **************/
/*                                             */
#define offsetX     0    // OFFSET values
#define offsetY     0
#define offsetZ     0

define gainX      1    // GAIN factors

define gainY      1

define gainZ      1

I am sorry if I am just being slow or if I am not clear on this, but I performed the calibration steps and the results for the 6 tests were:

Accel Minimums: -4  0  0
Accel Maximums: 0  3  276

Accel Minimums: -4  0  0
Accel Maximums: 12  258  276

Accel Minimums: -250  0  -6
Accel Maximums: 12  258  276

Accel Minimums: -250  -259  -6
Accel Maximums: 12  258  276

Accel Minimums: -250  -259  -6
Accel Maximums: 264  258  276

Accel Minimums: -250  -259  -230
Accel Maximums: 264  258  276

What I am missing is how do I go from those calibration results to the offset and gain values as per their formula?

Best overview here: https://edwardmallon.wordpress.com/2015/05/22/calibrating-any-compass-or-accelerometer-for-arduino/

I did a similar calibration using the SparkFun guide.

I made a little excel spreadsheet with the values (such as the ones at the bottom of your serial port's readout): +1g -1g Gain Offset X 246 -268 257 -5.5 Y 243 -264 253.5 -5.25 Z 238 -265 251.5 -6.75

The gain and offset values are from the two equations you posted: For example: Gain for x = 0.5*(236-(-268)) and Offset for x = 0.5*(236+(-268)).

How did it work out for you? I'm still not getting the results I was expecting exactly (with the default increments of 62.5 mg per increment my z-axis is reading ~30 which looks like ~1.8g).