The source code

    function generateData(){
        var data = [];
        for(var i = 0; i < 12; ++i){
            data.push([Date.monthNames[i], (Math.floor(Math.random() *  11) + 1) * 100]);
        }
        return data;
    }

    Ext.onReady(function(){
        var store = new Ext.data.ArrayStore({
            fields: ['month', 'hits'],
            data: generateData()
        });

        new Ext.Panel({
            width: 700,
            height: 400,
            renderTo: document.body,
            title: 'Column Chart with Reload - Hits per Month',
            tbar: [{
                text: 'Load new data set',
                handler: function(){
                    store.loadData(generateData());
                }
            }],
            items: {
                xtype: 'columnchart',
                store: store,
                yField: 'hits',
                xField: 'month',
                xAxis: new Ext.chart.CategoryAxis({
                    title: 'Month'
                }),
                yAxis: new Ext.chart.NumericAxis({
                    title: 'Hits'
                }),
                extraStyle: {
                   xAxis: {
                        labelRotation: -90
                    }
                }
            }
        });
    });