bmpGraphics.DrawLine(blackpen, oldX, lastPlottedValue, oldX++, newValue)

pictureBox_graph.Refresh()

private void port_DataReceived() 
        {
            while(port.InBufferCount > 1) 
            {
                // Read two bytes from port and save them as a short in the array
                dataStorage[recievedValues++] = BitConverter.ToInt16(port.Input, 0);

                // Update the GUI every 10th reception
                if(recievedValues % 20 == 0) 
                {
                    try 
                    {
                        this.Invoke(new EventHandler(updateGUI));
                    }
                    catch(Exception e) 
                    {
                        Console.WriteLine(e.Message);
                    }
                }
            }
        }

        private void updateGUI(object o, EventArgs e) 
        {
            // Update the recieved values label.
            label2.Text = recievedValues.ToString();
            // Draw the graph
            drawGraph();
        }


        private void hScrollBar1_ValueChanged_1(object sender, System.EventArgs e)
        {
            this.graph_panel.Left = -this.hScrollBar1.Value;
        }

        private void drawGraph() 
        {
            // Do this as many times as there's unplotted values.
            for(int i = 0; i < recievedValues - plottedValues; i++) 
            {
                // Calculate new y-value to plot
                int y2 = (int)((dataStorage[plottedValues + 1] - short.MinValue) / yscale);

                // Draw a line from last plotted point to the one calculated above
                bmpGraphics.DrawLine(blackpen, plottedValues, lastPlottedValue, plottedValues + 1, y2);

                // Increase plotted values counter
                plottedValues++;

                // Save the plotted value to use as starting point for next line
                lastPlottedValue = y2;

                // Set the scroll bar into right position
                hScrollBar1.Maximum = plottedValues - hScrollBar1.Width; // Should be width of something else, but it didn't work =(
                hScrollBar1.Value = hScrollBar1.Maximum;

            }
            pictureBox_graph.Refresh();
        }
    }