>>>>
>>>>With that correction the heading does seems to remain fairly constant regardless of beta and gamma values. But changes on the x axis still result in the skip :-{
>>>>H
>>>
>>>
>>>Can you post the values of( alpha, beta, gamma , absolute) before and those that produce a 'skip' ?
>>>
>>>Update : and your current code
>>
>>result: 83.22823217922902 alpha:192.3341040127786 beta: -0.397645519862364 gamma: -4.076214696522571
>>result: 275.89877882326147 alpha:167.6809889302929 beta: 0.4615772773377466 gamma: -4.0949466064380005
>>
>>with a minute movement between the two consecutive readings. I note the beta went positive on the second result....
>>
>>Current code:

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);
>>    var compassHeading = Math.atan2(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)
>>}
>>

called from orientation changed event:

lastOrientation = compassHeading2(data.alpha, data.beta, data.gamma, data.absolute);
>>            console.log('result: ' + lastOrientation + 'alpha:'+data.alpha+ ' beta: '+data.beta + ' gamma: '+data.gamma);

>
>Viv,
>
>With the code below, this is the output I get
>

> 186.771767820771
> 174.101221176738
>

>
>What do you get ?
>
>I'm not too sure about your testing Vx, and Vy to add Math.PI or 2 * Math.PI since atan2 returns a value between -PI and +PI
>

>	class Test_atan
>	{
>		internal static void Go()
>		{
>			List<Value> list = new List<Value>()
>			{
>				new Value(192.3341040127786, -0.397645519862364, -4.076214696522571),
>				new Value(167.680988930292, 0.4615772773377466,-4.0949466064380005)
>			};
>			
>			// 186.771767820771
>			// 174.101221176738
>
>			foreach( Value v in list)
>			{
>				double degrees = DeviceOrientation(v.Alpha, v.Beta, v.Gamma);
>				Console.WriteLine(degrees);
>			}
>
>		}
>		static double DeviceOrientation(double alpha, double beta, double gamma)
>		{
>			double xRads = DegreeToRadian(beta);
>			double yRads = DegreeToRadian(gamma);
>			double zRads = DegreeToRadian(alpha);
>
>			double cX = Math.Cos(xRads);
>			double cY = Math.Cos(yRads);
>			double cZ = Math.Cos(zRads);
>
>			double sX = Math.Sin(xRads);
>			double sY = Math.Sin(yRads);
>			double sZ = Math.Sin(zRads);
>
>			// Calculate Vx and Vy components
>			var vx = -cZ * sY - sZ * sX * cY;
>			var vy = -sZ * sY + cZ * sX * cY;
>	
>			var compassHeading = Math.Atan2(vy, vx);
>			if (compassHeading < 0.0)
>				compassHeading += Math.PI + Math.PI;
>
>			return RadianToDegree(compassHeading);
>
>
>
>		}
>		static double DegreeToRadian(double degrees)
>		{
>			return Math.PI * Modulo(degrees, 360.00) / 180.0;
>
>		}
>		static double RadianToDegree(double rads)
>		{
>			return Modulo(rads, Math.PI * 2) * (180.0 / Math.PI);
>		}
>		static double Modulo(double dividend, double divisor)
>		{
>			return (dividend % divisor)
>				+ (Math.Sign(dividend) * Math.Sign(divisor) >= 0 ? 0 : divisor);
>		}
>
>		struct Value
>		{
>			internal readonly double Alpha;
>			internal readonly double Beta;
>			internal readonly double Gamma;
>
>			internal Value( double alpha, double beta, double gamma)
>			{
>				Alpha = alpha;
>				Beta = beta;
>				Gamma = gamma;
>			}
>		}
>	}
>

Thx. Won't get a chance to look at this properly until tomorrow am - I'll get back to you.
First day I've spent where debugging involves a lot of waving my arms about with frequent breaks to untwist a USB cable.
More like being at a keep fit aerobics class :-}