Depreciation allocation: systematic charge of depreciable amount over useful life with consistent method and disclosure. Depreciation requires systematic allocation of an asset's depreciable amount over its estimated useful life, based on historical cost or substituted amount, useful life and residual value. Useful life is an estimate affected by legal limits, physical wear, usage and obsolescence and must be reviewed periodically; revisions require prospective allocation of the remaining unamortised amount. Methods (e.g., straight-line or reducing balance) must be applied consistently; changes are treated as accounting policy changes, recalculated from asset commissioning with adjustments and disclosed. Financial statements must disclose methods, depreciation totals, accumulated depreciation and relevant cost or revalued amounts.