Align first point Y-axis in line chart

[Hoowling]

Hi,

I have a graph where the stock price development for a selected stock is presented compared to an index. 
To be able to assess the relative performance vs the index I would like to align the starting points in the graph. 

This would mean that the red line (index) starts at the same place as the blue line (stock), highlighted in the yellow cirle. 
Any ideas on how to achieve this?

Also, I recognise the problem of scale when evaluating relative performance. How would I set up the graph so that the performance can be evaluated and that the graph changes dynamically when selections are made (e.g. selection of different stocks, time periods etc.). 

Thanks! 

//Hoowling