Private Sub Worksheet_Change(ByVal Target As Range)
    If Not Intersect(Target, Range("a1")) Is Nothing Then
        a = Target.Value
        If a <> "" Then
            u = Cells(Rows.Count, "a").End(xlUp).Row + 1
            Range("a" & u) = a
            Range("a1").ClearContents
            Range("a1").Select
        End If
    End If
End Sub

Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.Count > 1 Then Exit Sub
    If Target.Address(0, 0) <> "A1" Then Exit Sub
    If Target = "" Then Exit Sub
    r_ = Cells(Rows.Count, 1).End(3).Row + 1
    Application.Calculation = 3
    Application.EnableEvents = 0
    Cells(r_, 1) = Target
    Target.ClearContents
    Application.EnableEvents = 1
    Application.Calculation = 1
    Target.Select
End Sub