Accumulated Depreciation

  In the user guide says:

"If you are adding an asset that you have already depreciated, you can enter the accumulated depreciation as of the last depreciation run date for this book, or let Oracle Assets calculate it for you"

I have an asset whose the date placed in service   is 27-JUL-2010, I put in accumulated depreciation 0.00.   In running the depreciation, but the accumulated depreciation has only the monthly depreciation value, not the value  that they should have based on their  date placed in service (27-jul-2010).  My open period is July-2011.  12 months have passed
How do I get Oracle calculate the correct value of accumulated depreciation, considering their date placed in service?