Public Function NormDist(ByVal x As Double, ByVal mean As Double, ByVal sd As Double) As Double
Dim x2 As Double = (x - mean) / sd
If X2 = 0 Then
Return 0.5
Else
Dim oor2pi As Double = 1 / Math.Sqrt(2.0 * Math.PI)
Dim t As Double = 1 / (1.0 + 0.2316419 * Math.Abs(x2))
t = t * oor2pi * Math.Exp(-0.5 * x2 * x2) * (0.31938153 + t * (-0.356563782 + t * (1.781477937 + t * (-1.821255978 + t * 1.330274429))))
If (x2>0)
Return 1.0 - t
Else
Return t
End If
End If
End Function