Help neede with ADXL345 low pass filter

Using Arduino Sensors
6 
Add these before setup():

byte i;
long reading[4]; // or unsigned long, if they are only positive numbers.

long will support ~ +/2.14 billion, unsigned long will support 0 to 4.29 billion

Then in loop();

   for (int i=0; i<4; i=i+1) {
    reading[i] = read_adxl();
   }

reading[0], reading[1], reading[2], and reading[3] will have your 4 values.