codice:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Documento senza titolo</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> 
<style type="text/css">
html,body{
	margin:0;
	padding:0;
}
#pre{
	background:#eee;
	height:1500px;
	padding:33px;
}
#target{
	background:#666;
	color:#fff;
	height:600px;
}
#scroll_amount{
	position:fixed;
	top:15px;
	right:15px;
	background:rgba(0,0,0,0.5);
	color:#fff;
	width:250px;
	padding:40px;
}
#scroll_amount:before{
	content:'Scroll pagina in pixel';
	font-weight:bold;
	display:block;
	margin-bottom:5px;
}
#shiva
{
  width: 100px;
	height: 100px;
	background: red;
	-moz-border-radius: 50px;
	-webkit-border-radius: 50px;
	border-radius: 50px;
  float:left;
  margin:5px;
}


.count
{
  line-height: 100px;
  color:white;
  margin-left:30px;
  font-size:25px;
}
</style>
<script type="text/javascript">
var target_top, screen_height, seen;
$(function(){
	seen=false;
	target_top=$('#target').offset().top;
	screen_height=$(window).height();
	$('#pre').append('<p>Posizione di #target: '+target_top+'px</p>');
	$('#pre').append('<p>Altezza finestra: '+screen_height+'px</p>');
	$('#pre').append('<p>Quantità di scroll per far apparire #target: '+Number(target_top-screen_height)+'px</p>');
});
$(window).scroll(function(){
	var scroll_amount=$(window).scrollTop();
	$('#scroll_amount').text(scroll_amount+'px');
	if(scroll_amount>=(target_top-screen_height)){
		if(!seen){
			increment();
			seen=true;
		}
		$('#scroll_amount').append('<p><strong>#target è visibile!</strong></p>');
	}else{
		$('#scroll_amount p').remove();
	}
});
function increment(){
  $('.count').each(function () {
    $(this).prop('Counter',0).animate({
        Counter: $(this).text()
    }, {
        duration: 4000,
        easing: 'swing',
        step: function (now) {
            $(this).text(Math.ceil(now));
        }
    });
});
}
</script>
</head>


<body>
<div id="pre"><h1>Above the fold</h1></div>
<div id="target"><div id="shiva"><span class="count">1000</span></div></div>
<div id="scroll_amount">0px</div>
</body>
</html>
Ho usato la variabile seen per eseguire l'animazione una sola volta.