arconic and subsidiaries notes to the consolidated financial statements ( dollars in millions , except per-share amounts ) a . summary of significant accounting policies basis of presentation . the consolidated financial statements of arconic inc . and subsidiaries ( 201carconic 201d or the 201ccompany 201d ) are prepared in conformity with accounting principles generally accepted in the united states of america ( gaap ) and require management to make certain judgments , estimates , and assumptions . these may affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements . they also may affect the reported amounts of revenues and expenses during the reporting period . actual results could differ from those estimates upon subsequent resolution of identified matters . certain prior year amounts have been reclassified to conform to the current year presentation . the separation of alcoa inc . into two standalone , publicly-traded companies , arconic inc . ( the new name for alcoa inc. ) and alcoa corporation , became effective on november 1 , 2016 ( the 201cseparation transaction 201d ) . the financial results of alcoa corporation for all periods prior to the separation transaction have been retrospectively reflected in the statement of consolidated operations as discontinued operations and , as such , have been excluded from continuing operations and segment results for all periods presented prior to the separation transaction . the cash flows and comprehensive income related to alcoa corporation have not been segregated and are included in the statement of consolidated cash flows and statement of consolidated comprehensive ( loss ) income , respectively , for all periods presented . see note c for additional information related to the separation transaction and discontinued operations . principles of consolidation . the consolidated financial statements include the accounts of arconic and companies in which arconic has a controlling interest . intercompany transactions have been eliminated . investments in affiliates in which arconic cannot exercise significant influence are accounted for on the cost method . management also evaluates whether an arconic entity or interest is a variable interest entity and whether arconic is the primary beneficiary . consolidation is required if both of these criteria are met . arconic does not have any variable interest entities requiring consolidation . related party transactions . arconic buys products from and provides services to alcoa corporation following the separation at negotiated prices between the parties . these transactions were not material to the financial position or results of operations of arconic for all periods presented . effective may 2017 , upon disposition of the remaining common stock that arconic held in alcoa corporation , they are no longer deemed a related party . cash equivalents . cash equivalents are highly liquid investments purchased with an original maturity of three months or less . inventory valuation . inventories are carried at the lower of cost and net realizable value , with cost for approximately half of u.s . inventories determined under the last-in , first-out ( lifo ) method . the cost of other inventories is determined under a combination of the first-in , first-out ( fifo ) and average-cost methods . properties , plants , and equipment . properties , plants , and equipment are recorded at cost . depreciation is recorded principally on the straight-line method at rates based on the estimated useful lives of the assets . the following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment ( numbers in years ) : .
what is the variation between the useful lives of the structures and machinery and equipment by the global rolled products segment?
gains or losses from the sale of assets are generally recorded in other income , net ( see policy below for assets classified as held for sale and discontinued operations ) . repairs and maintenance are charged to expense as incurred . interest related to the construction of qualifying assets is capitalized as part of the construction costs . properties , plants , and equipment are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets ( asset group ) may not be recoverable . recoverability of assets is determined by comparing the estimated undiscounted net cash flows of the operations related to the assets ( asset group ) to their carrying amount . an impairment loss would be recognized when the carrying amount of the assets ( asset group ) exceeds the estimated undiscounted net cash flows . the amount of the impairment loss to be recorded is calculated as the excess of the carrying value of the assets .