Hey there.

First of all, great work on the library! Wonderful library.

I have a question, how do I go about if I want to hold two points between a chart (line or area), and I'll see the percent change between them? Like if you were to type a stock in google finance, and hold two points together, you'll see what I mean. Below are two images, one from Google Finance, and the other from Apple Stocks. I believe the Apple Stocks one (second image) does the effect better.

Thanks.