Samples of calculating standard deviation in .NET(C#/VB.NET).

StdDevExtension.cs

static class Extensions
{
    public static double StdDev(this IEnumerable<double> src)
    {
        IList<double> lst = src is IList<double> ? (IList<double>)src : src.ToArray();
        int n = lst.Count();
        double ave = lst.Average();
        double s = 0;
        for (int i = 0; i < n; ++i)
            s = s + (lst[i] - ave) * (lst[i] - ave);
        return Math.Sqrt(s / n);
    }
}

StdDevExtension.vb

Module Extensions

    <Extension()>
    Public Function StdDev(src As IEnumerable(Of Double)) As Double
        Dim lst As IList(Of Double) = If(TypeOf src Is IList(Of Double), CType(src, IList(Of Double)), src.ToArray())
        Dim n As Integer = lst.Count()
        Dim ave As Double = lst.Average()
        Dim s As Double = 0
        For i As Integer = 0 To n - 1
            s = s + (lst(i) - ave) * (lst(i) - ave)
        Next
        Return Math.Sqrt(s / n)
    End Function

End Module