private void btnFormGVShowDialog_Click(object sender, EventArgs e)
 {
     for (int i = 0; i < NumWin; i++)
     {
         using (FormGV f2 = new FormGV(_dt))
         {
             f2.ShowDialog();
         }
     }
 }
        private void btnFormGVShow_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < NumWin; i++)
            {
                FormGV f1 = new FormGV(_dt);
                f1.Show();

                if (!SpeedTest)
                {
                    while (!f1.IsDisposed)
                    {
                        Application.DoEvents();
                        System.Threading.Thread.Sleep(100);
                    }
                }
            }
        }