VS 2010 How to detect character position (index) of click in RichTextBox

Public Class frmPhoneme
 
    Private Sub PhonemePress(sender As System.Object, e As System.EventArgs) Handles Button1.Click, Button2.Click, Button3.Click,
        Button4.Click, Button5.Click, Button6.Click, Button7.Click, Button8.Click, Button9.Click, Button10.Click, Button11.Click,
        Button12.Click, Button13.Click, Button14.Click, Button15.Click, Button16.Click, Button17.Click, Button18.Click, Button19.Click,
        Button20.Click, Button21.Click, Button22.Click, Button23.Click, Button24.Click, Button25.Click, Button26.Click, Button27.Click,
        Button28.Click, Button29.Click, Button30.Click, Button31.Click, Button32.Click, Button33.Click, Button34.Click, Button35.Click,
        Button36.Click, Button37.Click, Button38.Click, Button39.Click, Button40.Click, Button41.Click, Button42.Click, Button43.Click,
        Button44.Click, Button48.Click, Button50.Click, Button51.Click
        Dim Btn As Button = DirectCast(sender, Button)
        RichTextBox1.Text += Btn.Tag.ToString
    End Sub
 
    Private Sub Button46_Click(sender As System.Object, e As System.EventArgs) Handles Button46.Click
        RichTextBox1.Text = ""
    End Sub
 
    Private Sub Button49_Click(sender As System.Object, e As System.EventArgs) Handles Button49.Click
        Me.Close()
    End Sub
 
    Private Sub Button47_Click(sender As System.Object, e As System.EventArgs) Handles Button47.Click
        Clipboard.SetDataObject(RichTextBox1.Text, True)
    End Sub
 
    Private Sub RichTextBox1_Click(sender As Object, e As System.EventArgs) Handles RichTextBox1.Click
 
    End Sub
 
    Private Sub RichTextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles RichTextBox1.TextChanged
 
    End Sub
End Class