Power Pivot: Adding a measure to a Pivot Chart

First time using Power Pivot!

I've broken my date down into histogram bins by adding a calculated column to the Data Model. I've also added a measure to my table for calculating the average of a specific column - I want this to be global and not break down into my histogram bins. How do I do this? This is what I have

MeanRadialScaleFactor70000:=average([ScaleFactor_R_70000])

but it's calculating the value for each histogram bin, not globally. This is what I have...

Capture.JPG

What I want is this, but with additional lines indicating the global mean for each line.

Please help, thanks