What are the straight line and written down value methods of depreciation?

In the straight line method, the same amount is charged every year: (cost minus residual value) divided by useful life. In the written down value method, a fixed percentage is charged on the opening book value each year, so the charge is higher in early years and falls over time.

For example, an asset costing Rs 1,00,000 depreciated at 10% on WDV has a charge of Rs 10,000 in year one and Rs 9,000 in year two. Note that the Income Tax Act has its own prescribed rates and block-of-assets rules, which can differ from the depreciation you book in your accounts.