private void interpolation_Click(object sender, EventArgs e)
        {
            if (form.Visible == false)
            {
                try
                {
                    form.Visible = true;
                    if (i > 0)
                    {
                        i--;
                    }
                }
                catch (System.ObjectDisposedException)
                {
                    i++;
                }
            }
            else
            {
                MessageBox.Show("The Window is already opened ", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }

            if ((i > 0) && (form.Visible == false))
            {
                form         = new interpolation();
                form.Visible = true;
            }
        }
        private void interpolation_Click(object sender, EventArgs e)
        {
            if (form.Visible == false)
            {
                try
                {
                    form.Visible = true;
                    if (i > 0)
                        i--;
                }
                catch (System.ObjectDisposedException)
                {
                    i++;

                }
            }
            else
                MessageBox.Show("The Window is already opened ", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

            if ((i > 0) && (form.Visible == false))
            {
                form = new interpolation();
                form.Visible = true;
            }
        }