Function NormInv(ByVal Probability As Double, ByVal Mu As Double, ByVal _
      Sigma As Double)
 
        Dim x As Double
        Dim p As Double
        Dim c0 As Double, c1 As Double, c2 As Double
        Dim d1 As Double, d2 As Double, d3 As Double
        Dim t As Double
        Dim q As Double
        q = Probability
        If (q = 0.5) Then
            NormInv = Mu
        Else
            q = 1.0# - q
 
            If ((q > 0) And (q < 0.5)) Then
                p = q
            Else
                If (q = 1) Then
                    p = 1 - 0.9999999 ' JPR - attempt to fix divide by zero 
                    ' below, what is NormInv(1,x,y)?
                Else
                    p = 1.0# - q
                End If
            End If
 
            t = Sqrt(Log(1.0# / (p * p)))
 
            c0 = 2.515517
            c1 = 0.802853
            c2 = 0.010328
 
            d1 = 1.432788
            d2 = 0.189269
            d3 = 0.001308
 
            x = t - (c0 + c1 * t + c2 * (t * t)) / (1.0# + d1 * t + d2 * (t * _
              t) + d3 * (t ^ 3))
            If (q > 0.5) Then
                x = -1.0# * x
            End If
        End If
        NormInv = (x * Sigma) + Mu
    End Function