var lastScrollY=0;     
function heartBeat(){    
var diffY;     
if (document.documentElement && document.documentElement.scrollTop)     
    diffY = document.documentElement.scrollTop;     
else if (document.body)     
    diffY = document.body.scrollTop     
else     
    {/*Netscape stuff*/}     
         
percent=.1*(diffY-lastScrollY);      
if(percent>0)percent=Math.ceil(percent);      
else percent=Math.floor(percent);      
document.getElementById("adleft").style.top=parseInt(document.getElementById("adleft").style.top)+percent+"px";     

lastScrollY=lastScrollY+percent;      
}     
   
function adhide(names){document.getElementById(names).style.display='none';}    
function screencl(names){if(screen.width<=800){adhide(names);}}    
zcode="<div id='adleft' style='left:3px;position: absolute;z-index:1;top:120px;'><iframe scrolling='no' width='95' height='350' src='http://www.zltrain.com/ad/left.htm' frameborder='0'></iframe></div>";    
 
document.write(zcode);    
  
screencl('adleft');      
window.setInterval("heartBeat()",1);