Question: How to find zero position/origin for Qtcharts graph

Hello,
I am trying to find a function to get the position value of the zero position or origin in QtchartsSpline chart.
The red dot in this graph is the position I would like to find out.
http://i.imgur.com/ZLh59ft.pngusing globalPos(), windowPos(), and pos() cannot seem to find the position of the origin.
Thank you.