How do I add a LineSeries to a 100% stacked bar chart while my ColumnSeries stay stacked to 100% with amCharts? - amcharts4

Question

I have several stacked column series displayed as "totalPercent".
For example:
var series = chart.series.push(new am4charts.ColumnSeries());
series.dataFields.valueY = "footfall";
series.dataFields.valueYShow = "totalPercent";
series.dataFields.dateX = "datetime";
These display properly.
I'm trying to add a line to my series' of stacked columns.
For example:
var trend = chart.series.push(new am4charts.LineSeries());
trend.dataFields.valueY = "benchline";
trend.dataFields.dateX = "datetime";
trend.data = [ {"datetime": new Date(2021, 3, 23, 10),"benchline": 65},
{"datetime": new Date(2021, 3, 24, 13),"benchline": 65},
{"datetime": new Date(2021, 3, 26, 13),"benchline": 65}];
trend.strokeWidth = 2
trend.stroke = trend.fill = am4core.color("#c00");
trend.legendSettings.labelText = "Demos benchmark";
The 'benchline' values get included in the total from which the 'totalPercent' is calculated for the stacked columns, squashing the first 3 (same number as I have points in my LineSeries).
Is there some way to include the LineSeries without distorting the columns?
Fiddle with full code.

Answer 1

The trick was to add a second axis and attach the LineSeries to that axis.
var valueAxis2 = chart.yAxes.push(new am4charts.ValueAxis());
valueAxis2.title.text = "Percent";
valueAxis2.renderer.opposite = true;
valueAxis2.min = 0;
valueAxis2.max = 100;
valueAxis2.strictMinMax = true;
valueAxis2.renderer.labels.template.adapter.add("text", function(text) {
return text + "%";
});
var trend = chart.series.push(new am4charts.LineSeries());
trend.dataFields.valueY = "benchline";
trend.dataFields.dateX = "datetime";
trend.data = [ {"datetime": new Date(2021, 3, 23, 10),"benchline": 65},
{"datetime": new Date(2021, 3, 24, 13),"benchline": 65},
{"datetime": new Date(2021, 3, 26, 13),"benchline": 65}];
trend.strokeWidth = 2
trend.stroke = trend.fill = am4core.color("#c00");
trend.legendSettings.labelText = "Demos benchmark";
trend.yAxis = valueAxis2;