Adding additional data to a single point

[Hutch]

Hey,

A novice coder here. Was wondering if it is possible to show a third data point in the information when scrolling across the point. 

Its easier to explain in pictures, 

I want to turn this:

Into something like this: 

But I only want the mean visable when scrolling over the point.   
Here's the example graph so far: https://jsfiddle.net/api/post/library/pure/