请问这句话的意思-tdiv.style.pixelTop>=tdiv.offsetHeight*1

function move1(whichdiv)
{
tdiv=eval(whichdiv)
if (tdiv.style.pixelTop>0&&tdiv.style.pixelTop<=car_num)  //如果顶部的距离大于零并且小于每次移动的距离的话，就直接使顶部距离为0.
 {
  tdiv.style.pixelTop=0
  setTimeout("move1(tdiv)",pausebetweenimages)
  setTimeout("move2(second2)",pausebetweenimages)
  return
  }
if (tdiv.style.pixelTop>=tdiv.offsetHeight*-1) //不明白这句话的意思。
 {
  tdiv.style.pixelTop-=car_num
  setTimeout("move1(tdiv)",50)
 }
else
 {
  tdiv.style.pixelTop=scrollheight
  tdiv.innerHTML=slideimages[0]
  if (i==slideimages.length-1)
  i=0
  else i++
 }
}
function move2(whichdiv)
{
  tdiv2=eval(whichdiv)
  if (tdiv2.style.pixelTop>0&&tdiv2.style.pixelTop<=car_num)
   {
    tdiv2.style.pixelTop=0
    setTimeout("move2(tdiv2)",pausebetweenimages)
    setTimeout("move1(first2)",pausebetweenimages)
    return
   }
 if (tdiv2.style.pixelTop>=tdiv2.offsetHeight*-1)
  {
   tdiv2.style.pixelTop-=car_num
   setTimeout("move2(second2)",50)
  }
 else
  {
   tdiv2.style.pixelTop=scrollheight
   tdiv2.innerHTML=slideimages[1]
    if (i==slideimages.length-1)
    i=0
    else 
    i++
  }
}
function conmouse(){car_num=0;} //鼠标经过时图片停止

function cmouseout(){car_num=5;}  //鼠标离开时继续按原来的速度上移。

function startscroll()

{
  
  move1(first2)
  second2.style.top=scrollheight

}

</SCRIPT>