HMC5883L compass / Arduino, start and remember 1st head...

// HMC5883L-COMPASS-1st-Angle-stored

#include <Arduino.h>
#include <Wire.h>
#include <HMC5883L_Simple.h>

// Create a compass
HMC5883L_Simple Compass;
int Read1stAngle = 0;
int StartAngle = 0;

void setup()
{
  Serial.begin(115200);
  Wire.begin();

  // The declination for your area can be obtained from http://www.magnetic-declination.com/
  Compass.SetDeclination(-0, 23, 'W');

  // The device can operate in SINGLE (default) or CONTINUOUS mode
  //   SINGLE simply means that it takes a reading when you request one
  //   CONTINUOUS means that it is always taking readings
  // for most purposes, SINGLE is what you want.
  Compass.SetSamplingMode(COMPASS_SINGLE);

  // The scale can be adjusted to one of several levels, you can probably leave it at the default.
  // Essentially this controls how sensitive the device is.
  //   Options are 088, 130 (default), 190, 250, 400, 470, 560, 810
  // Specify the option as COMPASS_SCALE_xxx
  // Lower values are more sensitive, higher values are less sensitive.
  // The default is probably just fine, it works for me.  If it seems very noisy
  // (jumping around), incrase the scale to a higher one.
  Compass.SetScale(COMPASS_SCALE_130);

  // The compass has 3 axes, but two of them must be close to parallel to the earth's surface to read it,
  // (we do not compensate for tilt, that's a complicated thing) - just like a real compass has a floating
  // needle you can imagine the digital compass does too.
  //
  // To allow you to mount the compass in different ways you can specify the orientation:
  //   COMPASS_HORIZONTAL_X_NORTH (default), the compass is oriented horizontally, top-side up. when pointing North the X silkscreen arrow will point North
  //   COMPASS_HORIZONTAL_Y_NORTH, top-side up, Y is the needle,when pointing North the Y silkscreen arrow will point North
  //   COMPASS_VERTICAL_X_EAST,    vertically mounted (tall) looking at the top side, when facing North the X silkscreen arrow will point East
  //   COMPASS_VERTICAL_Y_WEST,    vertically mounted (wide) looking at the top side, when facing North the Y silkscreen arrow will point West
  Compass.SetOrientation(COMPASS_HORIZONTAL_Y_NORTH);

}

// Our main program loop.
void loop()
{
  float heading = Compass.GetHeadingDegrees();

  Serial.print("Heading: \t");
  Serial.print( heading );
  Serial.print(" / StartAngle: ");
  Serial.print(StartAngle);
  Serial.print(" / Read1stAngle: ");
  Serial.print(Read1stAngle);
  Serial.println();

  //Store start angle
  if ( Read1stAngle == 0 ) {
    StartAngle = heading;
    Read1stAngle = 1;
  }
  // END store startangle

  delay(100);
}