One of the basic stock chart features for amcharts\yahoo\google charts is to recalculate a percent axis during comparisons.

http://www.amcharts.com/stock-chart/
https://www.amcharts.com/tutorials/disabling-or-enabling-value-axis-recalculation-to-percents/

The stockchart should be more of a widget that allows comparisons that automatically converts to percents during comparisons.

For example, in the amcharts you can add\remove stocks easily, and when there are two stocks to compare it automatically shifts to a percent axis. The chart itself does the calculations as they are very standard.

For us, this would also need to work in a virtual MVC scenario.

Currently, we have to do the calculations either on the client\server, insert\remove\hide\show price\percent axis and legend info etc....just to duplicate other charts that are built in with these features.