>I'm trying to get accurate heading information from the deviceorientation event.
>
>Till now I've just been using the alpha value and generally this is good but occasionally the heading will 'flick' a random number of degrees. I'm assuming this is because it needs to be corrected with the y and z axis values (beta,gamma). I've tried using the following code (from http://w3c.github.io/deviceorientation/spec-source-orientation.html ) :

var degtorad = Math.PI / 180; // Degree-to-Radian conversion
>
>function compassHeading2(alpha, beta, gamma , absolute) {
>
>    var _x = beta ? beta * degtorad : 0; // beta value
>    var _y = gamma ? gamma * degtorad : 0; // gamma value
>    var _z = alpha ? alpha * degtorad : 0; // alpha value
>
>    var cX = Math.cos(_x);
>    var cY = Math.cos(_y);
>    var cZ = Math.cos(_z);
>    var sX = Math.sin(_x);
>    var sY = Math.sin(_y);
>    var sZ = Math.sin(_z);
>
>    // Calculate Vx and Vy components
>    var Vx = -cZ * sY - sZ * sX * cY;
>    var Vy = -sZ * sY + cZ * sX * cY;
>
>    // Calculate compass heading
>    var compassHeading = Math.atan(Vx / Vy);
>
>    // Convert compass heading to use whole unit circle
>    if (Vy < 0) {
>        compassHeading += Math.PI;
>    } else if (Vx < 0) {
>        compassHeading += 2 * Math.PI;
>    }
>
>    return compassHeading * (180 / Math.PI); // Compass Heading (in degrees)
>}

but, instead of improving matters, this results in even more wildly erratic behaviour.
>
>I'm testing on a Nexus 7 with Chrome browser. The hardware seems OK (Nexus apps showing a compass are smooth and accurate).
>Anyone know what the problem may be (or of an existing html page that demonstrates good results) ?


(1) Is the output of compassHeading2() correct ?
(2) How terrible is 'erratic'
(3) assuming (1) is ok, what is your update frequency ?
(4) Didn't you have a similar question in the past ( also with a Nexus) ?