How to setup depreciation method for special requirements

Hi all
I have a requirement to set up new depreciation method to calculate depreciation in such way:
For example, Cost=3000, rate=1%

First month depreciation=3000*1%=30; Accumulated depreciation=30
Second month depreciation=(3000-30)*1%=29,7; Accumulated depreciation=30+29,7=59,7
Third month depreciation=(3000-59,7)*1%=29,4; Accumulated depreciation=59,7+29,4=89,1
etc

How to setup such method? As I understand I need to use method type=FLAT, Calculation basis=NBV... But I can't get required depreciation amounts for example above...