protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
    {
        CheckBox chk = (CheckBox) sender;

        DataControlFieldCell dcf = (DataControlFieldCell)chk.Parent;
        GridViewRow gvr = (GridViewRow)dcf.Parent;

        if (chk.Checked)
        {
            Label lab = (Label)gvr.Cells[3].FindControl("Label1");
            lab.Text = "T";
        }
        else
        {
            Label lab = (Label)gvr.Cells[3].FindControl("Label1");
            lab.Text = "";
        }
    }