function minproduction() {
   if (document.getElementById) {
      ww = parseInt(document.getElementById('pcbwidth').value) + 3;
      hh = parseInt(document.getElementById('pcbheight').value) + 3;
      minnum = 500000/(ww*hh);
      altminnum = Math.round(500000/(ww*hh));
      if (minnum!=altminnum) minnum = Math.round(0.5 + 500000/(ww*hh));
      if (!isNaN(minnum)) document.getElementById('pcbminimum').value = minnum;
   }
}