public class StdDev
{
	public double calcMean(double [] numbers)
	{
		double sum;
		double avg;
		
		// accumulate the sum
		sum = 0;
		
		for (int ii = 0; ii < numbers.length; ii++)
		{
			sum = sum + numbers[ii];
		}
		
		avg = sum / numbers.length;
		
		return avg;
	}
	
	public double calcStdDev(double [] numbers)
	{
		double avg;
		double sumSquares;
		double stdDev;
		
		// first get avg
		avg = calcMean(numbers);
		
		// sum the differences squared
		sumSquares = 0;
		
		for (int ii = 0; ii < numbers.length; ii++)
		{
			sumSquares = sumSquares + 
				Math.pow((numbers[ii] - avg), 2);
		}
		
		stdDev = Math.sqrt((sumSquares / numbers.length));
		
		return stdDev;
	}
}