window.onload = function () {

        var chart = new CanvasJS.Chart("chartContainer", {
            title: {
                text: "Temperature over time"
            },
        axisX:{
            title: "time",
                    valueFormatString: "YYYY-DD-MM HH:mm:ss",
            },
        axisY: {
                title: "temperature [°C]"
            },
            data: [{
                type: "line",
                dataPoints: <?php echo json_encode(array_reverse($ydata1), JSON_NUMERIC_CHECK); ?>
            }]
        });
        chart.render();