add an eqution to a custom property

Hi,

I have a custom property that references the parts surface area, however the results are given in mm² and I want them to show as m².

My document setting are for mm which I want to keep so how do I change this result only to show as M².

The idea is to have the surface area M² show in a drawing.

Thanks

Mark (SolidWorks 2015 sp4)

SolidworksDrawings And Detailing