Revenue Recognition We recognize revenue when the four basic criteria for recognition are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services rendered; (3) consideration is fixed or determinable; and (4) collectability is reasonably assured. Sales of products We provide for the sale of our products, including disposable processing sets and supplies to customers. Revenue from the sale of products is recognized upon shipment of products to the customers. We do not maintain a reserve for returned products as in the past those returns have not been material. Usage or leasing of blood separation equipment As a result of the acquisition of the Angel® business in 2010, we acquired various multiple element revenue arrangements that combine the (i) usage or leasing of blood separation processing equipment, (ii) maintenance of processing equipment, and (iii) purchase of disposable processing sets and supplies. We assigned these multiple element revenue arrangements to Arthrex on August 7, 2013. (See Note 3 ? Distribution and License Agreement with Arthrex for additional details.) Under these arrangements, the total arrangement consideration was allocated to the various elements based on their relative estimated selling prices. The usage of the blood separation processing equipment was accounted for as an operating lease; since customer payments were contingent upon the customer ordering new products, rental income was recorded following the contingent rental method when rental income was earned and collectability was reasonably assured. The sale of disposable processing sets and supplies and maintenance were deemed a combined unit of accounting; since (a) any consideration for disposable processing sets and supplies and maintenance was contingent upon the customer ordering additional disposable processing sets and supplies and (b) both the disposable products and maintenance services were provided over the same term, we recognized revenue for this combined unit of accounting followi