System.Drawing Problem in c#

 // 

        /// Shows the coordinates of the mouse whenever it moves
        /// 
        /// 
        /// 
        private void Graph_MouseMove(object sender, MouseEventArgs e)
        {
            Double x, y;

            // Get the coordinates and set them according to the axises
            x = (e.X - this.Width/2);
            y = (this.Height/2 - e.Y);

            // Display them on the intended labels
            TSxLBL.Text = "X = " + (x/10).ToString("F1");
            TSyLBL.Text = "Y = " + (y/10).ToString("F1");

            // Check if the specific coordinate exists in the function, if so, show the "Function Point" TB
            if (Exists(ref _points, e.Location))
                FuncPntLBL.Visible = true;
            else
                FuncPntLBL.Visible = false;
        }