How to get date and time in point height chart?

Question

I draw tall charts on the page. This works great but I have a small problem, it seems to me that when I hover over it I don't get the date and time.

This is what my json looks like:

[{"measurement value":"measurement value","date":"date","data":["9/5/2022",14.6,"9/5/2022" ,14.8,"6 -9-2022",15.948,"2022/9/6",17.112,"2022/9/6",

My chart looks like this:

You see the balloon on the left, it shows the number 0: 14.6.14.6 is the value, which is fine, but 0 is a number for that value, like another point, giving

But how do I display the date and time that the number in the balloon belongs to?

我的图表代码是这样的：

$.getJSON("mfrmetingen300RG.json", function(data) {
                const processedData9 = [];

                for (let a = 0; a < data[0].data.length; a  = 2) {
                    processedData9.push([data[0].data[a], data[0].data[a   1]]);
                }

                data[0].data = processedData9;
                avg = <?php echo $rowj[0]; ?>;
                StDev = <?php echo $rowj[1]; ?>;
                Aantalwaarden9 = <?php echo $rowj[2]; ?>;
                //Cp=(USL-LSL)/(6xstd.Dev) see.:https://www.easycalculation.com/statistics/learn-cp-cpk-calculator.php
                //Cpk = (USL-gemiddelde) / (3 x std.Dev) of (gemiddelde-LSL) / (3 x std.Dev)

                cpkl1 = (<?php echo $_cpkh10waarde; ?>-<?php echo $_cpkl10waarde; ?>)/(6*StDev);
                Cpk1High = (<?php echo $_cpkh10waarde; ?>-avg)/(3*StDev);
                Cpk1Low = (avg-<?php echo $_cpkl10waarde; ?>)/(3*StDev);

                chart9 = new Highcharts.Chart('container9',{
                    chart: {
                        zoomType: 'x',
                        type: 'line',
                        marginRight: 130,
                        marginBottom: 100,
                        backgroundColor:'azure'
                    },
                    rangeSelector: {
                        buttons: [{
                            text: ' ',
                            events: {
                                click() {
                                    return false
                                }
                            }
                        },
                        {
                            text: '-',
                            events: {
                                click() {
                                    return false
                                }
                            }
                        }]
                    },
                    title: {
                        useHTML: true,
                            text: "Gemeten MFR waarde van PP 300R Grey Extrusie over de laatste " (Aantalwaarden9) " waarden.",

                         x: -20 //center
                    },
                    credits: {
                        enabled: false
                    },
                    subtitle: {text: 'Gem.=' avg.toFixed(2) ' Stdev=' StDev.toFixed(2) ' Cp=' cpkl1.toFixed(2) ' Cpk_High=' Cpk1High.toFixed(2) ' Cpk_Low=' Cpk1Low.toFixed(2) '',x: -20},
                    xAxis: {
                        uniqueNames: false,
                        type: 'category',
                        title: {
                            text: 'Datum'
                        }
                    },
                    yAxis: {
                        "min":15,
                        "max":23,
                        title: {
                            text: 'MFR'
                        },
                        plotLines: [{
                            value: 0,
                            width: 1,
                            color: '#808080'
                        }],
                        plotLines: [{value: <?php echo $_cpkl10waarde; ?>,color: <?php echo $_color_min_line; ?>,dashStyle: 'longdashdot',width: 2,label: {text: 'Minimum'}},
                                    {value: <?php echo $_cpkh10waarde; ?>,color: <?php echo $_color_max_line; ?>,dashStyle: 'longdashdot',width: 2,label: {text: 'Maximum'}},
                                    {value: <?php echo $_cpkm10waarde; ?>,color: <?php echo $_color_guide_line; ?>,dashStyle: 'shortdash',width: 2,label: {text: 'Richtlijn'}},
                                    {value: avg.toFixed(2),color: <?php echo $_color_avg_line; ?>,dashStyle: 'spline',width: 2,label: {text: 'Avg'}},
                        ]
                    },
                    tooltip: {
                        formatter: function() {
                            return '<b>Meetwaarden</b><br/>'  this.x  ': '  this.y;
                        }
                    },
                    legend: {layout: 'vertical',align: 'right',verticalAlign: 'top', x: -100,y: 0,floating: true,borderWidth: 0},
                    series: data,
                    plotOptions: {
                        line: {
                            dataLabels: {
                                enabled: true
                            }
                        }
                    },
                });
                chart9.legend.allItems[0].update({name:'MFR'});
            }, 1000);
        });```

Answer 1

Because you have category type xAxis, your category name is contained in the point.key variable. So based on your example you only need to reference this.key

tooltip: {
  formatter: function() {
      return '<b>Meetwaarden</b><br/>'+ this.key +': '+ this.y;
  }
},

Simplified demonstration: https://jsfiddle.net/BlackLabel/87bousnL/

API Reference: https://api.highcharts.com/highcharts/tooltip.headerFormat