Painting Chart

private void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            int a, b, c, d = 0;
            a = int.Parse(numericUpDown1.Value.ToString());
            b = a * 3600;
            c = b / 1000;
            d = 50;
            SolidBrush sb = new SolidBrush(Color.Black);
            Bitmap bit = new Bitmap(Width, Height);
            Graphics g = Graphics.FromImage(bit);
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            g.DrawPie(new Pen(sb, 1), d, 20, 190, 170, 0, 360);
            sb.Color = Color.Silver;
            g.FillPie(sb, d, 20, 190, 170, 0, 360);
            sb.Color = Color.Black;
            g.DrawPie(new Pen(sb, 1), d, 20, 190, 170, -c, c);
            sb.Color = Color.Yellow;
            g.FillPie(sb, d, 20, 190, 170, -c, c);
            this.BackgroundImage = bit;

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            numericUpDown1_ValueChanged(null, null);
        }