Depreciation key for additions

Dear All,

We have a requirement with asset depreciation...

Client needs the depreciation to be calculated for the 6 months to be 17.5% and next 6 months to be 35%.

Current year 2009

Additions for this year (Plant-Asset Class)

First 183 days - Depreciation should calculate 17.5%

Second 182 days - Depreciation should calculate 35%

How this can be achived