Plotting serial port data using zedgraph

namespace WindowsApplication2
{
    public partial class Form1 : Form
    {
        // All members variables should be placed here
        // make it more readable..

        string t;
        SerialPort sp;

        Thread m_thread;
        bool m_running = false;
        ManualResetEvent m_event = new ManualResetEvent(true);
        bool m_pause = false;
        private GraphPane myPane;

        public Form1()
        {
            InitializeComponent();
            Control.CheckForIllegalCrossThreadCalls = false;
            // User can already search for ports when the constructor of the FORM1 is calling 
            // And let the user search ports again with a click
            // Searching for ports function

            SearchPorts();

            CreateZedGraph(); //error : Severity	Code	Description	Project	File	Line	Suppression State
                              //Error CS7036  There is no argument given that corresponds to the required formal parameter 
                              //'w' of 'Form1.DrawPoint(ZedGraphControl, int, PointPair)'
        }
        // start button
        private void btnStart_Click(object sender, EventArgs e)
        {
            if (m_thread == null || m_thread.IsAlive == false)
            {
                ClearGraph();
                m_thread = new Thread(Process);
                m_thread.Start();
            }
        }
        void Process()
        {       
            PointPair point = new PointPair();
            btnStart.Enabled = false;
            btnStop.Enabled = true;
            m_running = true;
            while (m_running == true)
            {
                m_event.WaitOne();
                
                point.Y = Convert.ToDouble(serialPort1);
                point.X++;  //time instance of measurement??
                DrawPoint(zed1, point);
                ssData.Value = point.Y.ToString();
                RefresheZedGraphs(zed1);
                Thread.Sleep(700);
            }
            btnStart.Enabled = true;
        }

        private void CreateZedGraph(object sender, SerialDataReceivedEventArgs e, ZedGraphControl zgc)
        {
            myPane = zgc.GraphPane;
            // axes stuff
            myPane.Title.Text = "FRDM-KW40z serial Test";
            myPane.XAxis.Title.Text = "Time";
            myPane.YAxis.Title.Text = "Voltage";
            myPane.XAxis.MajorGrid.IsVisible = true;
            myPane.YAxis.MajorGrid.IsVisible = true;
            myPane.XAxis.MinorGrid.IsVisible = true;
            myPane.YAxis.MinorGrid.IsVisible = true;

            // data from serial port
            
            PointPairList list = new PointPairList();
            zed1.GraphPane.AddCurve("Test", list, Color.Red);

        }

private void button2_Click(object sender, EventArgs e)
        {
            comboBox1.Items.Clear();
            SearchPorts();
        }
        void SearchPorts()
        {
            string[] ports = SerialPort.GetPortNames();
            foreach (string port in ports)
            {
                comboBox1.Items.Add(port);
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
            // Catch exception if it will be thrown so the user will see it in a message box
            OpenCloseSerial();
        }      
        void OpenCloseSerial()
        {
            try
            {
                if (sp == null || sp.IsOpen == false)
                {
                    t = comboBox1.Text.ToString();
                    sErial(t);
                    button3.Text = "Close Serial port"; // button text
                }
                else
                {
                    sp.Close();
                    button3.Text = "Connect and wait for inputs";   // button text

                }
            }
            catch (Exception err)   // catching error message
            {
                MessageBox.Show(err.Message);   // displaying error message
            }           
        }
      
        void sErial(string Port_name)
        {
            try
            {
                sp = new SerialPort(Port_name, 115200, Parity.None, 8, StopBits.One);   // serial port parameters
                sp.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);
                sp.Open();
            }
            catch (Exception err)
            {
                throw (new SystemException(err.Message));
            }
        }
//
        private  void DataReceivedHandler(object sender,SerialDataReceivedEventArgs e)
        {

            // This below line is not need , sp is global (belongs to the class!!)
            //SerialPort sp = (SerialPort)sender;
            if (e.EventType == SerialData.Chars)
            {
                if (sp.IsOpen)
                {
                    string w = sp.ReadExisting();
                    if (w != String.Empty)
                    {
                        Invoke(new Action(() => Control.Update(w)));
                    }
                }
            }
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (sp == null || sp.IsOpen == false)
            {
                OpenCloseSerial();
            }
        }

        private void button3_Click_1(object sender, EventArgs e)
        {

        }

        private void button4_Click(object sender, EventArgs e)
        {
            SaveFileDialog saveFileDialog1 = new SaveFileDialog();
            saveFileDialog1.InitialDirectory = @"C:\Users\varman\Documents\";
            saveFileDialog1.Title = "Save text Files";
            saveFileDialog1.CheckFileExists = true;
            saveFileDialog1.CheckPathExists = true;
            saveFileDialog1.DefaultExt = "txt";
            saveFileDialog1.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*";
            saveFileDialog1.FilterIndex = 2;
            saveFileDialog1.RestoreDirectory = true;

            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                File.WriteAllText(saveFileDialog1.FileName, zed1.Text);
                zed1.Text = saveFileDialog1.FileName;
            }
        }