Loading ...Again - here is some info from the readme file in ACA2008 - my comments in italics
Spaces
Property Set Definitions
New automatic property set definitions have been added for spaces.
Base Perimeter Including Interferences
Gross Area Minus Interferences
Gross Perimeter Including Interferences
Net Area Minus Interferences
Net Perimeter Including Interferences
Usable Area Minus Interferences
Usable Perimeter Including Interferences
Generate Spaces
When using the Generate all option [...]