highcharts tooltip programatically set always visible tooltip on latest point

1// Highcharts ==> Making always visible tooltip pointing to latest values
2// add this to load : functions settings
3chart_one.tooltip.refresh(chart_one.series[0].points[19]);
4
5// Highcharts ==> following is the sample which shows where to add the changes
6
7chart: {
8            type: 'spline',
9            backgroundColor: {
10                linearGradient: [0, 0, 500, 500],
11                stops: [
12                    [0, 'rgb(255, 255, 255)'],
13                    [1, 'rgb(200, 200, 255)']
14                ]
15            },
16            animation: Highcharts.svg, // don't animate in old IE
17            marginRight: 10,
18            
19            events: {
20                load: function () {
21
22                    // set up the updating of the chart each second
23                    var series = this.series[0];
24                    setInterval(function () {
25                        var x = (new Date()).getTime(), // current time
26                            y = a;
27                        series.addPoint([x, y], true, true);
28
29                        //for always on display value in tootip
30                      	// points[0] shows which point in the chart to show in tooltip
31                        chart_one.tooltip.refresh(chart_one.series[0].points[0]);
32                        //console.log("this chart "+ chart_one.series[0].points[0]);
33                    }, 3000);
34                }
35            }
36            
37        }