ElementStacks

HTML

<script src="http://highcharts.com/js/testing.js"></script>
<div id="container" style="height: 400px"></div>
<button>set new data</button>

JavaScript

window.chart = new Highcharts.Chart({
    chart: {
        renderTo: 'container'
    },
    series: [{
        data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1]
    }]
}, function(chart){

    var series = chart.series[0];
    
    $('button').click(function(){
        var data = series.data,
            new_data = (function(){
                for(var i=0,d=[];i<10;i++)
                    d.push(Math.random()*250|0)
                return d;
            })();
        
        console.log( series.data[data.length-1].x );
        alert(data[data.length-1].x);
        series.options.pointStart = data[data.length-1].x;
        series.setData(new_data);
    });

});