[code]
<script type="text/javascript">
var mouseDown = false;
var countType;
var counter = 0;
var nextTime;

function count()
{
    if (mouseDown)
    {
        if (isNaN(document.getElementById('aantal').value))
        {
            document.getElementById('aantal').value = 0;
        }
        counter++;
        if (countType)
        {
            document.getElementById('aantal').value ++;
        }
        else
        {
            document.getElementById('aantal').value --;
        }
        nextTime = 200 / counter;
        if (nextTime < 10)
        {
            nextTime = 10;
        }
        setTimeout('count();', nextTime);
    }
}

function startCount(type)
{
    mouseDown = true;
    countType = type;
    counter = 0;
    count();
}

function stopCount()
{
    mouseDown = false;
}
</script>


<style type="text/css">
#counter-container
{
    position: relative;
    width: 200px;
    border: 1px solid #ccc;
}

#up
{
    position: absolute;
    top: 0px;
    right: 0px;
}

#down
{
    position: absolute;
    bottom: 0px;
    right: 0px;
}

#aantal
{
    font: 11px verdana;
    border: 0;
}
</style>


<noscript>Voor deze functie is JavaScript nodig.</noscript>
<div id="counter-container">
    <input id="aantal" type="text" value="0" />
    <img id="up" src="up.gif" onmousedown="startCount(true);" onmouseup="stopCount();" onmouseout="stopCount();" />
    <img id="down" src="down.gif" onmousedown="startCount(false);" onmouseup="stopCount();" onmouseout="stopCount();" />
</div>
[/code]