Bar & Line
1 dimension + 2 metrics
The bar & line visualization grants the comparison of many different elements of the same dimension on two common metrics and is effective in exhibiting a time evolution.
This method allows you to see the correlation between two metrics.
A simple example
Let's say you want to see if an ad campaigns is effectively translating to greater web traffic and a higher number of visitors viewing your content. Adding a line representing your website bounce rate shows you whether your paid visits are efficient or if your visitors just leave your website as soon as they arrive.
Try it with your own data on the Visualization Playground
Let's analyze a bit
At a glance, we can see that even if your paid visits vary dramatically, your bounce rate remains relatively consistent over time.
You can still see, however, that the slight curve in the bounce rate correlates to the evolution of visits over time. The higher the amount of paid visits, the higher the bounce rate (and vice versa).
So is your campaign worth it?
Oh, and keep an eye on your bounce rate...it seems to be increasing over time.