wykres w c#

Witam
Mam taki problem z programem rysującym wykres ponieważ potrzebuje pobierać dane dla 2 różnych wykersow funkcji x y natomiast program pobiera mi tylko dane dla jednego wykresu oto kod programu proszę o pomoc.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using ZedGraph;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
double x1;
double x2;
double y2;
double y1;
List<Coordinate> _coordinates = new List<Coordinate>();
public Form1()
{
InitializeComponent();
}

    private void zedGraphControl1_Load(object sender, EventArgs e)
    {

    }


    private void Form1_Load(object sender, EventArgs e)
    {

        CreateGraph(zg1);

    }

    private void CreateGraph(ZedGraphControl zgc)
    {
        GraphPane myPane = zg1.GraphPane;
        // Set the titles and axis labels
        myPane.Title.Text = "Wykres";
        myPane.XAxis.Title.Text = "X";
        myPane.YAxis.Title.Text = "Y";
    }

    private void btnDraw_Click(object sender, EventArgs e)
    {
        if (!string.IsNullOrEmpty(tbCoordinateX.Text) && !string.IsNullOrEmpty(tbCoordinateY.Text))
        {
            try
            {
                double x = double.Parse(tbCoordinateX.Text);
                double y = double.Parse(tbCoordinateY.Text);
                double x1 = double.Parse(tBx1.Text);
                double y1 = double.Parse(tBy2.Text);
                double x2 = double.Parse(tbCoordinateX.Text);
                double y2 = double.Parse(tbCoordinateY.Text);
                

                Coordinate coordinate = new Coordinate(x, y);
                _coordinates.Add(coordinate);

                tbCoordinateY.Text = "";
                tbCoordinateX.Text = "";

                AddPoint(coordinate);

            }
            catch
            {
                MessageBox.Show("Błędne współżędne. Obecny punkt nie zostanie dodany do wykresu.");
            }
        }

        Clear();
        DrawCoordinates();


    }

    private void btnSet_Click(object sender, EventArgs e)
    {
        try
        {
            double x1 = double.Parse(tBx1.Text);
            double y1 = double.Parse(tBy2.Text);
            double x = double.Parse(tbCoordinateX.Text);
            double y = double.Parse(tbCoordinateY.Text);

            Coordinate coordinate = new Coordinate(x, y);
            _coordinates.Add(coordinate);

            tbCoordinateY.Text = "";
            tbCoordinateX.Text = "";
            tBy2.Text = "";
            tBx1.Text = "";

            AddPoint(coordinate);

        }
        catch (Exception ex)
        {
            MessageBox.Show("Błędne współżędne.");
        }
    }

    public void Clear()
    {

    }

    public void DrawCoordinates()
    {
        GraphPane myPane = zg1.GraphPane;
        //Make up some data points from the Sine function
        PointPairList list = new PointPairList();
        PointPairList list1 = new PointPairList();
        PointPairList list2 = new PointPairList();

        

        foreach (Coordinate item in _coordinates)
        {
            list.Add(item.X, item.Y);
            list1.Add(item.x1, item.y1);
            list2.Add(x2, y2);
        }



        Random random = new Random((int)DateTime.Now.Ticks);

        int r= random.Next(0, 255);
        int g= random.Next(0, 255);
        int b= random.Next(0, 255);


        //Generate a blue curve with circle symbols, and "My Curve 2" in the legend
        LineItem myCurve = myPane.AddCurve("Wartość", list, Color.FromArgb(255,r,g,b),
                          SymbolType.Circle);
        //Fill the area under the curve with a white-red gradient at 45 degrees
        myCurve.Line.Fill = new Fill(Color.White);
        // Make the symbols opaque by filling them with white
        myCurve.Symbol.Fill = new Fill(Color.White);

        //Fill the axis background with a color gradient
        myPane.Chart.Fill = new Fill(Color.White);

        // Fill the pane background with a color gradient
        myPane.Fill = new Fill(Color.White);
        zg1.Refresh();

        // Calculate the Axis Scale Ranges
    }

    private void btnReset_Click(object sender, EventArgs e)
    {
        //Reset _coordinates and clear the graph
        _coordinates = new List<Coordinate>();
        zg1.GraphPane.CurveList.Clear();
        zg1.Refresh();
        tbCoordinateY.Text = "";
        tbCoordinateX.Text = "";

        lbPoints.Items.Clear();
    }

    private void AddPoint(Coordinate coordinate)
    {
        lbPoints.Items.Add(string.Format("Punkt {0} ma współrzędne: X = {1} Y = {2}", _coordinates.Count, coordinate.X, coordinate.Y));
    }

    private void tBx1_TextChanged(object sender, EventArgs e)
    {

    }

    private void tBy2_TextChanged(object sender, EventArgs e)
    {

    }

}

}