How can we fix value in chart control - Y axis. Read Below:

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ASP.NET

I have generated a chart dynamically, which sets its y-axis value automatically on the basis of its numbers (generate dynamically on the basis of data). Suppose its value comes in 4 diffrent numbers i.e.(12,8,17,15) then it sets y-axis range upto 22 no. but when data comes in (12,8,21,19) then it sets y-axis range upto 25 no, but I want to fix its range 25 in every case. I am using this code :

string query = _query;
            SqlDataAdapter da = new SqlDataAdapter(query, con);
            DataTable dt = new DataTable();
            da.Fill(dt);
            string chart_name = System.DateTime.Now.Ticks + ".png";

            double[] yValues = { Convert.ToDouble(dt.Rows[0][1]), Convert.ToDouble(dt.Rows[1][1]), Convert.ToDouble(dt.Rows[2][1]), Convert.ToDouble(dt.Rows[3][1]) };
            string[] xValues = { dt.Rows[0][0].ToString(), dt.Rows[1][0].ToString(), dt.Rows[2][0].ToString(), dt.Rows[3][0].ToString() };

            double[] yValues2 = { Convert.ToDouble(dt.Rows[0][2]), Convert.ToDouble(dt.Rows[1][2]), Convert.ToDouble(dt.Rows[2][2]), Convert.ToDouble(dt.Rows[3][2]) };
            string[] xValues2 = { dt.Rows[0][0].ToString(), dt.Rows[1][0].ToString(), dt.Rows[2][0].ToString(), dt.Rows[3][0].ToString() };
            ChartArea chartArea = new ChartArea();
            Axis yAxis = new Axis(chartArea, AxisName.Y);
            Axis xAxis = new Axis(chartArea, AxisName.X);
            Chart1.Series["Current"].Points.DataBindXY(xValues, yValues);
            Chart1.Series["Preferred"].Points.DataBindXY(xValues2, yValues2);
            Chart1.Height = 250;
            Chart1.Width = 500;

            Chart1.AntiAliasing = AntiAliasingStyles.All;
            Chart1.TextAntiAliasingQuality = TextAntiAliasingQuality.High;
            using (var chartimage = new MemoryStream())
            {
                Chart1.SaveImage(Server.MapPath("~/images/" + chart_name), ChartImageFormat.Png);
                return chart_name;
            }

So if any body have an idea how can i fix Y-Axis data constantly (25), Kindly share with me.