>>>>So far, so good:

        public static void Main()
>>>>        {
>>>>            var result = GetAverage(new int[] {357, 2, 359, 356, 4, 2, 355, 22});  //Result : 2
>>>>            result = GetAverage(new int[] { 180, 182, 175, 178, 183, 185, 177, 172 });   //Result: 44 :-{
>>>>        }
>>>>
>>>>        public static double GetAverage(int[] values)
>>>>        {
>>>>            double c = 0;
>>>>            double s = 0;
>>>>
>>>>            foreach (int i in values)
>>>>            {
>>>>                double r = DegreeToRadian(i);
>>>>                c += Math.Cos(r);
>>>>                s += Math.Sin(r);
>>>>            }
>>>>
>>>>            double a = Math.Atan2(s, c);
>>>>
>>>>            return RadianToDegree(a);
>>>>        }
>>>>
>>>>        public static double DegreeToRadian(double angle)
>>>>        {
>>>>            return Math.PI * angle / 180.0;
>>>>        }
>>>>
>>>>        public static double RadianToDegree(double angle)
>>>>        {
>>>>            return angle * (180.0 / Math.PI);
>>>>        }

>>>> More testing......
>>>
>>>
>>>Took a bit of your code - adding vectors
>>>To my surprise Atan2() is clever - and returns the right quadrant
>>>
>>>

>>>		public static int GetAverage(IEnumerable<int> readings)
>>>		{
>>>			double s = 0.0, c = 0.0;
>>>			bool haveData = false;
>>>
>>>			foreach (int value in readings)
>>>			{
>>>				double rads = DegreeToRadian(value);
>>>				
>>>				s += Math.Sin(rads);
>>>				c += Math.Cos(rads);
>>>				haveData = true;
>>>			}
>>>			
>>>			int result = 0;
>>>			if (haveData)
>>>			{
>>>				double rads;
>>>
>>>				if (c == 0)
>>>				{
>>>					rads = s >= 0.00 ? Math.PI / 2.0 : -Math.PI / 2.0;
>>>				}
>>>				else
>>>					rads = Math.Atan2(s, c);
>>>
>>>				result  = (int)RadianToDegree(rads);
>>>
>>>			}
>>>			return result;
>>>		}
>>>		public static double DegreeToRadian(double degrees)
>>>		{
>>>			return Math.PI * Modulo(degrees, 360.00) / 180.0;
>>>		}
>>>
>>>		 public static double RadianToDegree(double rads)
>>>		{
>>>			return Modulo(rads, Math.PI * 2) * (180.0 / Math.PI);
>>>		}
>>>		public static double Modulo(double dividend, double divisor)
>>>		{
>>>			return (dividend % divisor)
>>>					+ (Math.Sign(dividend) * Math.Sign(divisor) >= 0 ? 0 : divisor);
>>>		}
>>>

I ended up with this (JScript):

function getAverageAngle(angleArray) {
>>    var c = 0;
>>    var s = 0;
>>    
>>    for (var i = 0; i < angleArray.length; i++) {
>>        var r = degreeToRadian(angleArray[i]);
>>        c += Math.cos(r);
>>        s += Math.sin(r);
>>    }
>>    var a = Math.atan2(s, c);
>>    var result = radianToDegree(a);
>>    if (result < 0)
>>        result = 360 + result;
>>    return result;
>>}
>>
>>function degreeToRadian(angle) {
>>    return Math.PI * angle / 180;
>>}
>>
>>function radianToDegree(angle) {
>>    return angle * (180 / Math.PI);
>>}

Raw and average seem to tally.
>
>
>Right - and to my surprise Atan2 also works when the cosine is zero

All now working smoothly (literally). I'm currently recalculating the average every time a new orientation event comes in. Processor seems to cope (g) and it makes for a very realistic damping effect.

Had a few moments panic but it turned out the device compass needed recalibrating - was getting some *very* strange results beforehand tho.

Thanks for the input and suggestions......