var LEFT = 125;
var MIN_LEFT = 105;
var cur_x;
var direction = -1;

function arrow()
{
  cur_x = LEFT;
  document.getElementById("arrow").style.top = (10 + document.getElementById("center").offsetTop + document.getElementById("warning").offsetTop) + "px";
  document.getElementById("arrow").style.left = LEFT + "px";
  document.getElementById("arrow").style.display = "block";
  setTimeout("movearrow()", 20);
}

function movearrow()
{
  if (cur_x < MIN_LEFT || cur_x > LEFT)
    direction *= -1;
  cur_x+=(1*direction);
  document.getElementById("arrow").style.left = cur_x + "px";
  setTimeout("movearrow()", 20);
}