float gdLatitudeDeg = (float) location.getLatitude();
float gdLongitudeDeg = (float) location.getLongitude();
float altitureMeters = (float) location.getAltitude();
// time
long timeMillis = System.currentTimeMillis();
// get the geo magnetic field
GeomagneticField geoField = new GeomagneticField(gdLatitudeDeg, gdLongitudeDeg, altitureMeters, timeMillis);
// calculate the field value now
float magHere = (float) Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2) + Math.pow(z, 2));
// calculate the expected
float magExpected = (float) Math.sqrt(geoField.getX() + geoField.getY() + geoField.getZ());