function resizeIndex() {

          var hb = getScreenHeight() - dy;
          var wb = Math.floor(hb * 470 / 300)
          var sw = getScreenWidth();
          var xb = Math.floor((sw - wb) / 2);
          var yt = 20 - hb;

          document.getElementById('a4').style.height = hb;
          document.getElementById('a4').style.width = wb;
          document.getElementById('a4').style.left = xb;
          document.images.ia4.style.height = hb;
          document.images.ia4.style.width = wb;
          document.images.ia4.style.left = xb;

          document.getElementById('a5').style.top = yt;
       }