Property Manager: formula for the allocated area in space assignment

Hello,

In property unit form, after I update the assignable area,  the corresponding area in space assignment form will be updated also.

I found that space assignment area = assignable area x % Area

This is just my guess. 

User guide just said it is based on assignable area and is dependant on % area field. 

Where can I get the formula of the allocated area in oracle documents (or API) ? 

Thanks in advance.

Regards,

Christine