Part II  note 1 principal accounting policies and related financial information the allowance is adjusted accordingly. The allowance for trade receivable  is $21.7 million and $18.2 million as of December 31, 2010 and 2009.  The provision to the allowance for trade receivables charged against  continuing operations was $4.3 million, $5.8 million and $3.1 million  for the years ended December 31, 2010, 2009 and 2008, respectively. the original estimate. Upon retirement of the long-lived asset, we either  settle the obligation for its recorded amount or incur a gain or loss. See  Note 8 for further discussion on our AROs. Investments in companies in which our ownership interest is 50 percent  or less and in which we exercise significant influence over operating and  financial policies are accounted for using the equity method. Under the  equity method, original investments are recorded at cost and adjusted  by our share of undistributed earnings and losses of these investments.  Majority owned investments in which our control is restricted are also  accounted for using the equity method. All other investments are carried  at their fair values or at cost, as appropriate. We are party to several joint  venture investments throughout the world, which individually and in the  aggregate are not significant to our financial results. Inventories are stated at the lower of cost or market value. Inventory costs  include those costs directly attributable to products before sale, including  all manufacturing overhead but excluding distribution costs. All domestic  inventories, excluding materials and supplies, are determined on a last-in,  first-out (“LIFO”) basis and our remaining inventories are recorded on a  first-in, first-out (“FIFO”) basis. See Note 5. We record property, plant and equipment, including capitalized interest,  at cost. Depreciation is provided principally on the straight-line basis over  the estimated useful lives of the assets (land improvements — 20 years,  buildings — 20 to 40 years, and machinery and equipment — 3 to 18  years). Gains and losses are reflected in income upon sale or retirement  of assets. Expenditures that extend the useful lives of property, plant and  equipment or increase productivity are capitalized. Ordinary repairs and  maintenance are expensed as incurred through operating expense. We review the recovery of the net book value of long-lived assets whenever  events and circumstances indicate that the net book value of an asset may  not be recoverable from the estimated undiscounted future cash flows  expected to result from its use and eventual disposition. In cases where  undiscounted expected future cash flows are less than the net book value,  we recognize an impairment loss equal to an amount by which the net book  value exceeds the fair value of the asset. Long-lived assets to be disposed of  are reported at the lower of carrying amount or fair value less cost to sell. We record asset retirement obligations at fair value at the time the liability  is incurred if we can reasonably estimate the settlement date. The associated  asset retirement obligations (“AROs”) are capitalized as part of the carrying  amount of related long-lived assets. In future periods, the liability is accreted  to its present value and the capitalized cost is depreciated over the useful  life of the related asset. We also adjust the liability for changes resulting  from the passage of time and/or revisions to the timing or the amount of  Definite life intangible assets consist primarily of patents, access rights,  customer relationships, registration rights, industry licenses, developed  formulations and other intangibles and are being amortized over periods  of 5 to 20 years. See Note 4 for additional information on goodwill and  intangible assets. Goodwill and other indefinite life intangible assets (“intangibles”) are  not subject to amortization. Instead, they are subject to at least an annual  assessment for impairment by applying a fair value-based test. We test goodwill for impairment annually using the criteria prescribed  by U.S. GAAP accounting guidance for goodwill and other intangible  assets. We did not record any goodwill impairments in 2010, 2009 and  2008. Based upon our annual impairment test, conducted in 2010, we  believe that the fair value of our reporting units with goodwill substantially  exceeds their carrying value. Unamortized capitalized software costs totaling $18.5 million and  $13.8 million at December 31, 2010 and 2009, respectively, are components  of other assets, which also include debt financing fees, advances to contract  manufacturers, recoveries related to environmental obligations (see Note 10),  intangibles assets other than goodwill (see Note 4), fair value of a deferred  compensation arrangement (see Note 17) and other deferred charges. We  capitalize the costs of internal use software in accordance with accounting  literature which generally requires the capitalization of certain costs incurred  to develop or obtain internal use software. We assess the recoverability of  capitalized software costs on an ongoing basis and record write-downs to  fair value as necessary. We amortize capitalized software costs over expected  useful lives ranging from three to ten years. We capitalized interest costs of $7.5 million in 2010, $3.8 million in  2009 and $5.7 million in 2008. These costs were associated with the  construction of certain long-lived assets and have been capitalized as  part of the cost of those assets. We amortize capitalized interest over  the assets’ estimated useful lives. Additionally, as part of these restructuring plans, write-downs of long-lived  assets may occur. Two types of assets are impacted: assets to be disposed  of by sale and assets to be abandoned. Assets to be disposed of by sale are  measured at the lower of carrying amount or estimated net proceeds from  the sale. Assets to be abandoned with no remaining future service potential  are written down to amounts expected to be recovered. The useful life of  assets to be abandoned that have a remaining future service potential are  adjusted and accelerated depreciation is recorded over the adjusted useful life. We continually perform strategic reviews and assess the return on our  businesses. This sometimes results in a plan to restructure the operations  of a business. We record an accrual for severance and other exit costs under  the provisions of the relevant accounting guidance. restructuring and other charges investments inventories Capitalized interest goodwill and intangible assets impairments of long-lived assets property, plant and equipment other assets asset retirement obligations 40 FMC Corporation    2010 Form 10K