Flat Rate depreciation on NBV

Hi All,

     How can depreciation can be changed so that it can be calculated on NBV on left out period of the Asset.

For Ex: An Asset is been purchsed from other Company and by detailed addition Cost and Accumulated Depreciation been added. On the NBV depreciation has to be split out on left period.

 Asset Cost 25000  Accumulated Deprectiation 22500. NBV is 2500 Life period in Months 5 ( Completed Asset life is not Known)

Depreciation has to 2500/5 i.e everymonth 100. How set up for depreciation can be done in this scenario.

Thanks,

Kishore.