floating reference lines in graph builder

[JMPinthePool]

What inspired this wish list request? 

I look at a lot of manufacturing process data, and often the data sets are very big, but sometimes we are interested in a relatively small number of data points.

What is the improvement you would like to see? 

It would be really cool if graph builder had this 'floating reference' line functionality, where you could add it and drag it about to where you're interested in order to easily see the associated values for each line - particularly useful if you have 'stacked' y-axes in graph builder - something i find i'm doing more and more. 

Why is this idea important? 

could be useful for anyone exploring time-stamped data