Private vData

Private Sub Worksheet_Change(ByVal Target As Range)
    On Error Resume Next
    If Not Intersect(Target, [H5:H100]) Is Nothing Then
        Application.EnableEvents = False
        If Target.Count = 1 And IsNumeric(Target(1)) Then
            Target = Target + vData
        Else
            Application.Undo
        End If
        Application.EnableEvents = True
    ElseIf Not Intersect(Target, Range("C2:C5")) Is Nothing And Target.Cells.Count = 1 Then
        Application.EnableEvents = False
        newVal = Target
        Application.Undo
        oldval = Target
        If Len(oldval) <> 0 And oldval <> newVal Then
            Target = Target & "," & newVal
        Else
            Target = newVal
        End If
        If Len(newVal) = 0 Then Target.ClearContents
        Application.EnableEvents = True
    End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Excel.Range)
    If Target.Count > 1 Then Exit Sub
    If Not Intersect(Target, [H5:H100]) Is Nothing Then
        If IsNumeric(Target) Then vData = Target
    End If
End Sub

If Not Intersect(Target, [E5:E100]) Is Nothing Then