Revenue Recognition Product revenue is recognized from contracts with customers when a customer has obtained control of a product. The Company considers control to have transferred based upon shipping terms. To the extent the Companys arrangements have a separate performance obligation, revenue related to any post-shipment performance obligation is deferred until completed. Shipping and handling costs charged to customers are included in total net sales and the associated expense is a component of cost of sales. Certain products are also sold through indirect distribution channels whereby the distributor assumes any further obligations to the end customer. Revenue is recognized on these distributor arrangements upon transfer of control to the distributor. Contracts do not contain variable pricing arrangements that are retrospective, except for rebate programs. Rebates are estimated based on expected sales volumes and offset against revenue at the time such revenue is recognized. The Company generally maintains the right to accept or reject a product return in its terms and conditions and also maintains appropriate accruals for outstanding credits. The related provisions for estimated returns and rebates are immaterial to the consolidated financial statements. Certain of the Companys product arrangements include separate performance obligations, primarily related to installation. Such performance obligations are accounted for separately when the deliverables have stand-alone value and the satisfaction of the undelivered performance obligations is probable and within the Company's control. The allocation of revenue between the performance obligations is based on the observable stand-alone selling prices at the time of the sale in accordance with a number of factors including service technician billing rates, time to install, and geographic location. Software is generally not considered a distinct performance obligation with the exception of a few small software applications. The Company generally does not sell software products without the related hardware instrument as the software is embedded in the product. The Companys products typically require no significant production, modification, or customization of the hardware or software that is essential to the functionality of the products. Service revenue not under contract is recognized upon the completion of the service performed. Revenue from spare parts sold on a stand-alone basis is recognized when control is transferred to the customer, which is generally at the time of shipment or delivery. Revenue from service contracts is recognized ratably over the contract period using a time-based method. These contracts represent an obligation to perform repair and other services including regulatory compliance qualification, calibration, certification, and preventative maintenance on a customers pre-defined equipment over the contract period.