Private Sub StepFnVerify()
    ' Test the StepFn function.

    Debug.Assert StepFn(12) = 1
    Debug.Assert StepFn(1) = 1
    Debug.Assert StepFn(0) = 0.5
    Debug.Assert StepFn(-1) = 0
    Debug.Assert StepFn(-12) = 0

    Debug.Assert IsNull(StepFn(Null))
    Debug.Assert IsNull(StepFn("Joe"))

End Sub