How about a basic tip?
I construct a QChart and render it on a QMainWindow using

chartView = new QChartView(_chart);

using baby steps here, I figured I could trap the chartViewws-> mouseMoveEvent by connecting it up to a slot:

connect(this, SIGNAL(chartView->mouseMoveEvent(QMouseEvent*)), this,SLOT(showPointToolTip(QMouseEvent*)));

but I get

No such signal HtcChart::chartView->mouseMoveEvent(QMouseEvent*)