Need Help!

I have some code below so that a div appears with my nav in when the user gets 680px down and hides again on the way back up. The problem is that on the way back up the div hides but once I get to the top of the window <0 it appears again to get rid I need to move down a few px to get rid of the div again. Whats missing!

<script>

$(window).scroll( function() {
if ( $(window).scrollTop() > 680 ) {
loadDiv2();
}
});

function loadDiv2() {
$('.nav_fade_wrapper').fadeIn('slow', function() {
$(this).fadeTo("fast", 1);
});
}

$(window).scroll(function(){
if($(window).scrollTop() < 720){
$(".nav_fade_wrapper").hide();
}

});
</script>