jQuery sparkline set interval array

Question

i have a script for showing span sparkline like this

function refresh_network() {
    var net = window.net = $('.dynamicbar').data('sparkline');
    $.getJSON('<?echo site_url('home / netinfo')?>', function (data)
    {
        var myvalues = [data.value, data.value, data.value, data.value, data.value, data.value, data.value];
        $('.dynamicbar').sparkline(myvalues, {
            type: 'line',
            barColor: 'green',
            width: '100px',
            height: '50px',
            fillColor: false,
            tooltipPrefix: 'RX ',
            chartRangeMin: 10000,
            chartRangeMax: 100000
        });
        var myvalues = [data.value2, data.value2, data.value2, data.value2, data.value2, data.value2, data.value2];
        $('.dynamicbar').sparkline(myvalues, {
            type: 'line',
            lineColor: 'red',
            width: '100px',
            height: '50px',
            composite: true,
            fillColor: false,
            tooltipPrefix: 'TX ',
            chartRangeMin: 10000,
            chartRangeMax: 100000
        });
    });

};

function auto_net() {
    refresh_network();
};

setInterval(auto_net, 500);

i have grep network (RX/TX). It change every 0.5 s, but i still confuse to show moving graph like this jsfiddle

But, in jsfiddle example. It's using ext.js(sencha), and the changing graph algorithm is using math random.

sparkline take parameter array like this [value1, value2, value3,..., valuex], example if i take 3 array then algorithm [value(now-2), value(now-1), value(now)]. But how to apply this?