Depreciation on written down value sets block-wise rates, special caps, and optional treatment for power-generation undertakings. Depreciation under the Income-tax Rules is computed on the written down value of blocks of assets used for the assessee's business or profession during the tax year, at the percentages specified in Appendix I, subject to stated exceptions and restrictions. For specified taxpayers, the allowance on a block of assets is capped at 40% of written down value where the prescribed option has been exercised or the stated conditions are satisfied. An undertaking engaged in power generation may opt for the general block-of-assets method instead of the special rate in Appendix II, and the option is final for subsequent tax years.