An impairment loss is recognized in the income statement whenever the carrying amount of an asset or its cash- generating unit exceeds its recoverable amount.  The recoverable amount of an asset is the greater of its fair value less costs to sell and its value-in-use. In assessing  value-in-use, an asset’s estimated future cash flows are discounted to their present value using a pre-tax discount  rate that reflects current market assessments of the time value of money and the risks specific to the assets/CGUs. In addition, the Group considers market data related to recent transactions for similar assets.  Subsequent costs are included in the asset’s carrying amount or recognised as a separate asset, as appropriate, only  when it is probable that future economic benefits associated with the item will flow to the group and the cost of the  item can be measured reliably. All other repairs and maintenance are charged to the consolidated statement of  profit or loss and comprehensive income during the financial period in which are they are incurred.  Property and equipment are depreciated on a straight-line basis over their useful lives from the time the asset is  held and ready for use. Leasehold improvements are depreciated over the shorter of either the unexpired period  of the lease or the estimated useful life of the improvement.  The depreciation rates used for each class of depreciable assets are:  The Group uses the units-of-production method to amortise costs carried forward in relation to its development and  production assets. For this approach, the calculation is based upon economically recoverable reserves, being proved  developed reserves and probable developed reserves, over the life of an asset or group of assets.  The assets’ residual values and useful lives are reviewed, and adjusted if appropriate, at the end of each reporting  period. An asset’s carrying amount is written down immediately to its recoverable amount if the asset’s carrying  amount is greater than its estimated recoverable amount, and recorded as impairment expense within the  consolidated statement of profit or loss and other comprehensive income.  Gains and losses on disposals are determined by comparing proceeds with the carrying amount. These gains and  losses are included in the statement of profit or loss.  The determination of whether an arrangement is, or contains, a lease is based on the substance of the arrangement  at date of inception. The arrangement is assessed to determine whether its fulfillment is dependent on the use of a  specific asset or assets and whether the arrangement conveys a right to use the asset, even if that right is not  explicitly specified in an arrangement.  Leases are classified as finance leases when the terms of the lease transfer substantially all the risks and benefits  incidental to the ownership of the asset, but not the legal ownership to the entities in the Group. All other leases  are classified as operating leases.  - 62 -  d) Leases  Depreciation and Amortisation Expense NOTE 1 - STATEMENT OF SIGNIFICANT ACCOUNTING POLICIES continued  NOTES TO THE CONSOLIDATED FINANCIAL STATEMENTS  Class of Non-Current Asset Depreciation Rate Basis of Depreciation  Plant and Equipment 10 – 33% Straight Line 