Object Growth Rate - Over What Time Period???

Looking at the Object Growth Rate page on the Performance Advisor for Windchill site.  What is the time period for the change?

The help documentation states the following:

"The Change In Count specifies the different in the current and the previous data counts for the business object."

I guess I'm not clear on what the "previous data" refers to.  Is this based on the "Windchill Database Statistics" logging interval?

6,118 new CAD Documents in a week seems like a lot (at least for our size company.)

P.S.  It would be really nice to get a graph showing the growth rate of each object type over different time intervals (month, year, 3 years, etc.)