Data display in Qchart

In my code, I use two QLineSeries to add data to QChart, their x Axis is the same.it is a DateTimeAxis,but Y Axis is different, then I want to show two series's values at the same time point.I found there is no such a function could do it,Anyone has good ideal?
for exmaple ,when I clicked on a series, I can get the value of this point in the serie,but how can I get another value of different serie which has the same DateTimeAxis.
In the PIC,I want to know two values of different series in the red line.

Once you have the X of one series you can iterate all values of the other values and search for the x and retrieve the Y:
std::tuple<bool,qreal> getYforX(const QXYSeries* const series, qreal xPoint){ for(int i=0;i<series>count();++i){ if(series>at(i).x()==xPoint) return std::make_tuple(true,series>at(i).y()); } return std::make_tuple(false,0.0); }

Thank you! it works.I'm just curious that there are no readymade functions