If I create two custom properties that are text and give them a value, I can combine them in a third custom property with the syntax $PRP:"customproperty" $PRP:"customproperty".

I can also combine two SolidWorks properties into one custom property as follows "SW-Mass(at)Part.SLDPRT" "SW-Density(at)Part.SLDPRT".  (Replace (at) with @)

I can even create an equation in the part as follows "kgs"="SW-Mass"*.454 and create a custom property to reference the equation using "kgs(at)Part.SLDPRT" (Replace (at) with @).

But I cannot combine two customer properties that are references to equations or combine to equations in a custom property.  What am I doing wrong?

I am on Windows 7 64-bit, SolidWorks 2010 SP5

Any help would be appreciated.

Thanks in advance.

Tim