Compare or overlay two separate graphs

I'd love some way to do a side-by-side or (even better) overlay comparison of two arbitrary graphs.

For example, there is no easy way to compare CPU usage on two different servers without adding them into a dashboard or perhaps opening two separate browser windows.

Obviously this is a relatively basic and contrived example, but I\'ve come across many times where something like this would be useful. Perhaps others have needed the same thing or have a better suggestion to cover this use case?