How to smooth moving from serial Port in c# ?

protected override void OnPaint(PaintEventArgs paintEvnt)
        {
            // Calling the base class OnPaint
            base.OnPaint(paintEvnt);


            // Clipping mask for Attitude Indicator
            paintEvnt.Graphics.Clip = new Region(new Rectangle(0, 0, 300, 300));
            paintEvnt.Graphics.FillRegion(Brushes.Black, paintEvnt.Graphics.Clip);


            // Make sure lines are drawn smoothly
            paintEvnt.Graphics.SmoothingMode = SmoothingMode.HighQuality;

            // Create the graphics object
            Graphics gfx = paintEvnt.Graphics;
           
            // Adjust and draw horizon image
            RotateAndTranslate(paintEvnt, mybitmap1, RollAngle, 0, ptBoule, (double)(4 * PitchAngle), ptRotation, 1);

            RotateAndTranslate2(paintEvnt, mybitmap3, YawAngle, RollAngle, 0, ptHeading, (double)(4 * PitchAngle), ptRotation, 1);

            gfx.DrawImage(mybitmap2, 0, 0); // Draw bezel image
            gfx.DrawImage(mybitmap4, 75, 125); // Draw wings image


            Graphics g = CreateGraphics();
            if (serialPort1.IsOpen == true)
            {
                g.FillEllipse(Brushes.Green, 20, 350, 20, 20);
            }
            else

                g.FillEllipse(Brushes.Red, 20, 310, 20, 20);


        }

 private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {

            // Obtain the number of bytes waiting in the port's buffer
            int bytes = serialPort1.BytesToRead;

            // Create a byte array buffer to hold the incoming data
             byte[] buffer = new byte[bytes];
            

            // Read the data from the port and store it in our buffer      
             serialPort1.Read(buffer, 0, bytes); //bytes
           
            Log(LogMsgType.Incoming, ByteArrayToHexString(buffer)); 
        
            if (bytes > 7 )//13
            {
                
                if (buffer[4] == 0)

                    PitchAngle = Convert.ToDouble(buffer[5]);
                else
                    PitchAngle = -1.0 * Convert.ToDouble(buffer[5]);

               
                Invalidate();
            }
    
        }