Depriciation as per companies act

This philosophy cant be accepted as a thumb of rule. If WDV rates and SLM rates of depreciation differ, residual value will be left. Regarding the timing of claiming your depreciation, when the asset is held for sale, if is not depreciated. But if the asset is retired, it means its fully depreciated and the deferred tax can arise. This salvage value has nothing to do with claiming depreciation

Depreciation simplified - Professional Resource | Industry (caclubindia.com)