Query on depreciation key configuration

Hi Experts

We have requirement to depreciate assets as below.

First 3 years asset will be depreciated at the rate of 20% per annum. At the end of 3 years, we need to evaluate every asset at that point in time to determine its remaining useful life. Remaining depreciation will be determined based on such evaluation. We will know the residual life of the asset only at the end of 3 years.

It would be of great help to let us know how to configure depreciation key for this requirement.

Regards,

Santosh