I find out some code from github.But it seems just use x and y axis data.This code work fine only the hmc5883l module horizontal placement.I think it’s not use Z axis reason right?

```
// Calculate heading
float heading = atan2(norm.YAxis, norm.XAxis);
// Set declination angle on your location and fix heading
// You can find your declination on: http://magnetic-declination.com/
// (+) Positive or (-) for negative
// For Bytom / Poland declination angle is 4'26E (positive)
// Formula: (deg + (min / 60.0)) / (180 / M_PI);
float declinationAngle = (4.0 + (26.0 / 60.0)) / (180 / M_PI);
heading += declinationAngle;
// Correct for heading < 0deg and heading > 360deg
if (heading < 0)
{
heading += 2 * PI;
}
if (heading > 2 * PI)
{
heading -= 2 * PI;
}
// Convert to degrees
float headingDegrees = heading * 180/M_PI;
```