about the unplanning depreciation

Hi friends

i met a requirement for unplanning dereciation

for example

Asset A orginal value 6000,scrap value 0,useful life 4 period

thus the plan depreciation for this 4 period is 1500 1500 1500 1500

when they do the unplanning 2500 for 1st period ,they can see the plan depreciation in 2nd period is also 1500 ,and in 3rd period is 500

but my client want to see the result is the plan depreciation in 2nd period is 1000 ,in 3rd period is also 1000

how can i set the depreciation key to realization it

now my customization in base value in multi level method is 24 and select the rem life

thanks a lot