Функция ниже подойдет?
Код:
Function Fnorm(x As Double) As Double
Const a = -0.366512920581664
Const b = -0.633732776724413
Const c = 0.813658012205085
Const d = 0.318769662544956
On Error GoTo Final
Fnorm = Exp(-Exp(a + b * x * (c + Exp(d * x))))
Exit Function
Final:
Fnorm = IIf(x < 0, 0, 1)
End Function
Ее нужно только прологарифмировать.