Public Function ErlangB(Servers As Single, Intensity As Single) As Single

Dim Val As Single, Last As Single, B As Single
Dim Count As Long, MaxIterate As Long
On Error GoTo ErlangBError
     If (Servers < 0) Or (Intensity < 0) Then
          ErlangB = 0
          Exit Function
     End If
     MaxIterate = Fix(Servers)
     Val = Intensity
     Last = 1 ' for server = 0
     For Count = 1 To MaxIterate
          B = (Val * Last) / (Count + (Val * Last))
          Last = B
     Next Count
ErlangBExit:
     ErlangB = MinMax(B, 0, 1)
     Exit Function
     
ErlangBError:
     B = 0
     Resume ErlangBExit
End Function