Depreciation on block of assets follows ownership, business use, written down value rules, and mandatory claim requirements. Depreciation applies to tangible and intangible assets owned wholly or partly by the assessee and used for business or profession, and is computed on the written down value of the relevant block of assets at the prescribed rate. Special rules provide proportionate reduction for partial business use, 50% depreciation where an asset is used for less than 180 days in the year of acquisition, and apportionment on succession, amalgamation or demerger. Depreciation is mandatory whether or not claimed, while goodwill is excluded and not eligible for depreciation.