C#

public partial class Form1 : Form
    {
        bool canResize;
        int mX, mY;
        Rectangle rect = new Rectangle();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.DrawRectangle(new Pen(Brushes.Purple, 2), rect);
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            canResize = true;
            mX = e.X; mY = e.Y;

            rect.Location = new Point(mX, mY);
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            canResize = false;
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (canResize)
            {
                if (mX < e.X)
                {
                    rect.X = mX;
                    rect.Width = e.X - mX;
                }
                else
                {
                    rect.X = e.X;
                    rect.Width = mX - e.X;
                }
                if (mY < e.Y)
                {
                    rect.Y = mY;
                    rect.Height = e.Y - mY;
                }
                else
                {
                    rect.Y = e.Y;
                    rect.Height = mY - e.Y;
                }
                this.Invalidate();
            }
        }
    }

//make sure curvelist has one curve
           if (zedGraphControl1.GraphPane.CurveList.Count <= 0)
               return;
           //Get first CurveItem in Graph
           LineItem curve = zedGraphControl1.GraphPane.CurveList[0] as LineItem;
           if (curve == null)
               return;
           // Get the PointPairList
           IPointListEdit list = curve.Points as IPointListEdit;
           // If this is null, it means the reference at curve.Points does not
           // support IPointListEdit, so we won't be able to modify it
           if (list == null)
               return;

           // Time is measured in seconds

           double time = (Environment.TickCount - tickStart) / 1000.0;


           // 3 seconds per cycle
           list.Add(time, dblLabel);

           // Keep the X scale at a rolling 30 second interval, with one
           // major step between the max X value and the end of the axis
           Scale xScale = zedGraphControl1.GraphPane.XAxis.Scale;
           if (time > xScale.Max - xScale.MajorStep)
           {
               xScale.Max = time + xScale.MajorStep;
               xScale.Min = xScale.Max - 30.0;
           }

           // Make sure the Y axis is rescaled to accommodate actual data
           zedGraphControl1.AxisChange();
           // Force a redraw
           zedGraphControl1.Invalidate();