设备像素比devicePixelRatio简单介绍

http://www.zhangxinxu.com/wordpress/2012/08/window-devicepixelratio/

var iScale = 1;
		iScale = iScale/window.devicePixelRatio;
		document.write('<meta name="viewport" content="width=device-width, initial-scale='+iScale+', maximum-scale='+iScale+', user-scalable='+iScale+'"');
		var iWidth = document.documentElement.clientWidth/16;
		document.getElementsByTagName('html')[0].style.fontSize = iWidth + 'px';
		document.getElementsByTagName('body')[0].style.fontSize = iWidth + 'px';