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amounts in excess of what we have recognized our effective tax rate in a given financial statement period could be materially affected. An unfavorable tax settlement might require use of our cash and/or result in an increase in our effective tax rate in the year of resolution. A favorable tax settlement would be recognized as a reduction in our effective tax rate in the year of resolution. Accounting for Stock-Based Compensation We account for awards of stock-based compensation under our employee stock-based compensation plans using the fair value method. Accordingly, we estimate the grant date fair value of our stock-based awards and amortize this fair value to compensation expense over the requisite service period or vesting term. We currently use the Black-Scholes option-pricing model to estimate the fair value of our stock option and ESPP awards. The determination of the fair value of stock-based awards on the date of grant using an option-pricing model is affected by our then current stock price as well as assumptions regarding a number of complex and subjective variables. These variables include the expected stock price volatility over the term of the awards, actual and projected employee stock option exercise behaviors, the risk-free interest rate and expected dividends. Due to the inherent limitations of option-valuation models, future events that are unpredictable and the estimation process utilized in determining the valuation of the stock-based awards, the ultimate value realized by award holders may vary significantly from the amounts expensed in our financial statements. For restricted stock and stock unit awards, grant date fair value is based upon the market price of our common stock on the date of the grant. This fair value is then amortized to compensation expense over the requisite service period or vesting term. We estimate expected forfeitures at the time of grant and revise this estimate, if necessary, in subsequent periods if actual forfeitures differ from initial estimates. Our determination of an estimated forfeiture rate is primarily based upon a review of historical experience but may also include consideration of other facts and circumstances we believe are indicative of future activity. The assessment of an estimated forfeiture rate will not alter the total compensation expense to be recognized, only the timing of this recognition as compensation expense is adjusted to reflect instruments that actually vest. If actual results are not consistent with our assumptions and judgments used in estimating key assumptions, we may be required to adjust compensation expense, which could be material to our results of operations. Recoverability of Long-Lived Assets We evaluate long-lived assets such as property, equipment and definite lived intangible assets, such as patents, for impairment whenever events or circumstances indicate that the carrying value of the assets recognized in our financial statements may not be recoverable. Factors that we consider include whether there has been a significant decrease in the market value of an asset, a significant change in the way an asset is being used, or a significant change, delay or departure in our strategy for that asset. Our assessment of the recoverability of long-lived assets involves significant judgment and estimation. These assessments reflect our assumptions, which, we believe, are consistent with the assumptions hypothetical marketplace participants use. Factors that we must estimate when performing recoverability and impairment tests include, among others, the economic life of the asset, sales volumes, prices, cost of capital, tax rates, and capital spending. These factors are often interdependent and therefore do not change in isolation. If impairment is indicated, we first determine if the total estimated future cash flows on an undiscounted basis are less than the carrying amounts of the asset or assets. If so, an impairment loss is measured and recognized. After an impairment loss is recognized, a new, lower cost basis for that long-lived asset is established. Subsequent changes in facts and circumstances do not result in the reversal of a previously recognized impairment loss. Our impairment loss calculations require that we apply judgment in estimating future cash flows and asset fair values, including estimating useful lives of the assets. To make these judgments, we may use internal discounted cash flow estimates, quoted market prices when available and independent appraisals as appropriate to determine fair value. If actual results are not consistent with our assumptions and judgments used in estimating future cash flows and asset fair values, we may be required to recognize additional impairment losses which could be material to our results of operations.