ACCESSでコントロールソースでの関数の使用について

    Public Function GetKinzoku(ByVal dtEntire As Date, ByVal dtRetire As Date) As TypeKinzoku
        Dim iDay As Integer
        iDay = DateTime.Day(dtRetire) - DateTime.Day(dtEntire)

        Dim iMonth As Integer
        iMonth = DateTime.Month(dtRetire) - DateTime.Month(dtEntire)

        Dim iYear As Integer
        iYear = DateTime.Year(dtRetire) - DateTime.Year(dtEntire)

        If iDay < -1 Then
            iMonth = iMonth - 1
        End If

        If iMonth < 0 Then
            iYear = iYear - 1
            iMonth = iMonth + 12
        End If

        If iYear < 0 Then
            iYear = 0
            iMonth = 0
        End If

        Dim tKinzoku As TypeKinzoku
        tKinzoku.Year = iYear
        tKinzoku.Month = iMonth

        Let GetKinzoku = tKinzoku
    End Function