Calcule d'une cellule selon une autre

Private Sub Worksheet_Change(ByVal Target As Range)
    Const TVA1 As Currency = 0.1
    Const colTTC = 20
    Const colTVA = 21
    Const colHT = 22
    Dim c As Range
    For Each c In Target
        If c.Row = 1 Or c.Row > 45 Or c = "" Then Exit Sub
        Application.EnableEvents = False
        Application.ScreenUpdating = False
        Select Case c.Column
        Case colHT ' HT
            Cells(c.Row, colTTC) = CCur(Cells(c.Row, colHT) * (1 + TVA1)) ' TTC
            Cells(c.Row, colTVA) = CCur(Cells(c.Row, colHT) * TVA1) ' TVA
        Case colTVA ' TVA
            If Target.Count = 1 Then Application.Undo
        Case colTTC ' TTC
            Cells(c.Row, colHT) = CCur(Cells(c.Row, colTTC) / (1 + TVA1)) ' HT
            Cells(c.Row, colTVA) = CCur(Cells(c.Row, colTTC) - Cells(c.Row, colHT)) ' TVA
        Case Else
            Exit Sub
        End Select
        Application.EnableEvents = True
    Next c
End Sub