[Observium] Show client *rate* on wireless clients graph

I'm using Observium to track wireless clients on our Cisco wireless controller. It's very useful. However, when I look at the longer-term graphs (monthly, yearly etc.) it's less useful because I'm not sure what it's showing. Is it clients per day, per week or what? For an example, see: https://dl.dropboxusercontent.com/u/3183918/apelmRwNW7.png.

Is there a way to get the legend show the rate rather than just a plain number?