Highcharts - 改变测量

Question

我有这张图表：http://jsfiddle.net/zf3m6/4/

我无法弄清楚如何更改“mm＆＃39;到＆＃39; km＆＃39;。

以下是当前代码：

$(function () {

    var tmpSerie = [{
        name: '20 and over',
        color: 'Red',
        data: [192]

    }, {
        name: 'Under 20',
        color: 'Green',
        data: [0, 173]

    }, {
        name: 'Zero',
        color: 'Blue',
        data: [0, 0, 25.1]

    }, {
        name: 'Not Assessed',
        color: 'Black',
        data: [0, 0, 0, 1.5]

    }],
        series = [],
        len = tmpSerie.length,
        i,j,data,dataLen;

    for (i = 0; i < len; i++) {
        data = [];
        dataLen = tmpSerie[i].data.length;

        for(j=0;j<dataLen;j++) {
            console.log(tmpSerie[i].data[j]);
            if(tmpSerie[i].data[j] > 0) {
                data.push(tmpSerie[i].data[j]);
            }
        }

        series.push({
            name: tmpSerie[i].name,
            color: tmpSerie[i].color,
            data: data
        });
    }

    $('#container').highcharts({
        chart: {
            type: 'column'
        },
        xAxis: {
            categories: [
                '20 and over',
                'Under 20',
                'Zero',
                'Not Assessed']
        },
        yAxis: {
            min: 0,




title: {
                text: 'Kilometers'
            }
        },
        tooltip: {
            headerFormat: '<span style="font-size:10px">{point.key}</span><table>',
            pointFormat: '<tr><td style="color:{series.color};padding:0">{series.name}: </td>' +
                '<td style="padding:0"><b>{point.y:.1f} mm</b></td></tr>',
            footerFormat: '</table>',
            shared: true,
            useHTML: true
        },
        plotOptions: {
            column: {
                pointPadding: 0.2,
                borderWidth: 0
            }
        },
        series: series
    });
});