Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        For outer As Integer = 1 To 5
            rtbTrace.AppendText("outer " & outer & ControlChars.NewLine)
            For inner As Integer = 10 To 50 Step 10
                rtbTrace.AppendText("    inner " & inner & ControlChars.NewLine)

            Next inner
        Next outer
    End Sub
End Class