Depreciation sale proceeds of fa under it act

If WDV of block of Assets exceeds sales value after the sale & other assets still exits, then sales valus(net of Taxes) should be deducted from WDV of block of asset

otherwise it may be short gain/losses as case may be 

Why cant we take wdv value instead of sale value for subtracting from gross block.

Gross Value find a significant place under Companies Act, 1956

But Under Income Tax Act 1961 only WDV are considered  for making any  reference relating to sale or transfer of fixed asset.