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## Use of Estimates 

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Some of the Company’s more significant estimates are those affected by critical accounting policies for revenue recognition, inventories and contingent liabilities. 

## Cash and cash equivalents 

Short-term investments that have a maturity of three months or less from the date of purchase are classified as cash equivalents. The Company invests excess cash in interest bearing accounts, money market mutual funds and funds which invest in U.S. Treasury obligations and repurchase agreements backed by U.S. Treasury obligations. The Company’s investment objectives continue to be the preservation of capital and the maintenance of liquidity. 

## Trade Receivables 

The Company maintains an allowance for doubtful accounts on trade receivables equal to amounts estimated to be uncollectible. This estimate is based upon historical collection experience combined with a specific review of each customer’s outstanding trade receivable balance. Management believes that the allowance for doubtful accounts is adequate; however, actual write-offs may exceed the recorded allowance. The following is a summary of activity relating to the allowance for doubtful accounts for the years ended December 31, 2012, 2013 and 2014: 

## Inventories 

<img src='content_image/245487.jpg'>

Inventory costs are determined principally by the use of the first-in, first-out (FIFO) costing method and are stated at the lower of cost or market. Company manufactured inventory is valued principally using standard costs, which are calculated based upon direct costs incurred and overhead allocations and approximate actual costs. Inventory purchased from third party vendors is principally valued at the weighted average cost. Periodically, obsolescence reviews are performed on slow-moving inventories and reserves are established based on current assessments about future demands and market conditions. The inventory values have been reduced by a reserve for excess and slow-moving inventories. Inventory reserves of $34.6 million and $33.2 million were recorded as of December 31, 2014 and 2013, respectively. If market conditions are less favorable than those projected by management, additional inventory reserves may be required. 

## Property, Plant and Equipment 

Property, plant and equipment are carried at cost, with depreciation provided on a straight-line basis over their estimated useful lives. 

