After Tax Equity Reversion example, understand, price

fishmarket

I don't get it, in the Douglas Manor Apartments example (Reading 47) when calculating the After Tax Equity Reversion, Depreciation is deducted twice. Firstly, it is deducted from Purchase price then it deducted from gain on the sale. Why is this so? There is no explantion as to why this was done.

Please help understand the logic here!