Subsequent Posting in In Existing Asset

Hi All

Please help on urgent.

I have Depreciation Up to date in Depreciation Key Check Box.

Now Suppose If i have on acquisition on 15.09.2011 say 100000 the system determine asset value date 15.09.2011 up to this point it is ok

but when i acquire new asset in existing asset code say on 15.12.2011 the system not calculated depreciation on addition value from 15.12.2011. instead of this system consider asset value date 15.09.2011. Please help i want to calculate depreciation from 15.12.2011 for subsequent acquisition.

Please help me

mann