Depreciation is the reduction in value of an asset due to wear and tear, age, or obsolescence. There are two main methods for calculating depreciation - straight line and written down value. The appropriate depreciation method depends on factors like the type and nature of the asset and prevailing business circumstances. Accounting standards require consistent application of the selected depreciation method each period. Changes to the depreciation method require recomputing depreciation from the date of acquisition and adjusting the accumulated depreciation. The objectives of depreciation accounting standards include uniformity in company accounts within a country and international comparability.