Deferred Commissions. Commissions incurred in acquiring new or renewal contracts are deferred and charged to operations as the related revenue is recognized. Forrester evaluates the recoverability of deferred commissions at each balance sheet date. Depreciation and Amortization. Forrester provides for depreciation and amortization, computed using the straight-line method, by charges to operations in amounts that allocate the costs of these assets over their estimated useful lives as follows: Product Development. All costs associated with the development of new products and services are expensed as incurred. Estimated Useful Life Computers and equipment 2 to 5 Years Computer software 3 Years Furniture and fixtures 7 Years Leasehold improvements Life of Lease Capitalized Software Costs. Statement of Position (SOP) No. 98-1,  Accounting for the Costs of Computer Software Developed or Obtained for Internal Use , requires certain computer software costs associated with internal-use software to be expensed as incurred until certain capitalization criteria are met. Forrester adopted SOP No. 98-1 beginning January 1, 1999. SOP No. 98-1 had no effect upon adoption. The net book value of capitalized internal use software costs at December 31, 1999 and 2000 was approximately $3,420,000 and $4,363,000, respectively. Comprehensive Income. Statement of Financial Accounting Standards (SFAS) No. 130,  Reporting Comprehensive Income , requires disclosure of the components of comprehensive income, which is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive income is disclosed in the accompanying statements of stockholders’ equity and comprehensive income. The components of accumulated other comprehensive income as of December 31, 1999 and 2000 are as follows (in thousands): 1999 2000 Unrealized (loss) gain on marketable securities, net of taxes $(413) $ 83 Cumulative translation adjustment (181) (439) Total accumulated other comprehensive loss $(594) $(356) Organizational Costs. In accordance with SOP No. 98-5,  Reporting on the Costs of Start-Up Activities , Forrester charges the costs of all startup activities, including organizational costs, to operations in the period in which those costs are incurred.  Concentration of Credit Risk. SFAS No. 105,  Disclosure of Information About Financial Instruments with Off-Balance-Sheet Risk and Financial Instruments with Concentrations of Credit Risk , requires disclosure of any significant off-balance-sheet and credit risk concentrations. Forrester has no significant off- balance sheet concentration of credit risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially subject Forrester to concentrations of credit risk are principally cash equivalents, marketable securities, and accounts receivable. Forrester places its investments in highly rated securities. No single customer accounted for greater than 10% of revenues or accounts receivable in any of the periods presented.