(function (doc, win) {  
  var docel = doc.documentelement,
    resizeevt = 'orientationchange' in window ? 'orientationchange' : 'resize', recalc = function () {
  var clientwidth = docel.clientwidth;
    if (!clientwidth) return;
      clientwidth = (clientwidth > 768 ) ? 768 : clientwidth ; docel.style.fontsize = 10 * (clientwidth / 375 ) + 'px';
    };
    if (!doc.addeventlistener) return; win.addeventlistener(resizeevt, recalc, false);
  recalc();
})(document, window);