android - Calculate difference between start angle and current measured angle/ Circle Calculation -

in application want calculate angle difference between start of application , current measured angle. therefore use sensor.type_accelerometer , sensor.type_magnetic_field current orientation. works quite well. here code:

@override public void onsensorchanged(sensorevent event) {     if (event.accuracy == sensormanager.sensor_status_unreliable)         return;     switch (event.sensor.gettype()) {     case sensor.type_accelerometer:         valuesaccelerometer = lowpass(event.values.clone(),                 valuesaccelerometer);         break;     case sensor.type_magnetic_field:         valuesmagneticfield = lowpass(event.values.clone(),                 valuesmagneticfield);     }     boolean success = sensormanager.getrotationmatrix(matrixr, matrixi,             valuesaccelerometer, valuesmagneticfield);     if (success) {         sensormanager.getorientation(matrixr, matrixvalues);         azimuth = (float) math.todegrees(matrixvalues[0]);         if (azimuth < 0.0f) {             azimuth += 360.0f;         }         if (!initaz) {             startazimuth = azimuth;             initaz = true;         } else {             float difaz = startazimuth-azimuth;             log.i("test", "" +"dif: "+ difaz +  "act_value " + azimuth + " start_value " + startazimuth);         }     }  } 

to describe problem here example logcat:

 dif: -220.63545    act_value 358.24    start_value 137.61  dif: -220.7943     act_value 358.40    start_value 137.61  dif: -221.49236    act_value 359.10    start_value 137.61  dif: 137.07309     act_value 0.53      start_value 137.61  dif: 135.63617     act_value 1.97      start_value 137.61  dif: 135.16443     act_value 2.44      start_value 137.61  dif: 136.15468     act_value 1.457     start_value 137.61  dif: 136.72552     act_value 0.88      start_value 137.61 

if current measurement turns 360° 0° difference angel turns wrong. how handle quite clean, works left , right rotation.