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 its 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. Under these arrangements, the total arrangement consideration is allocated to the various elements based on their relative estimated selling prices. The usage of the blood separation processing equipment is accounted for as an operating lease; since customer payments are contingent upon the customer ordering new products, rental income is recorded following the contingent rental method when rental income is earned and collectability is reasonably assured. The sale of disposable processing sets and supplies and maintenance are deemed a combined unit of accounting; since (a) any consideration for disposable processing sets and supplies and maintenance is contingent upon the customer ordering additional disposable processing sets and supplies and (b) both the disposable products and maintenance services are provided over the same term, we recognize revenue for this combined unit of accounting following the contingent revenue method at the time disposable products are delivered based on prices contained in the agreement. Rental income is currently less than 10 % of total revenue a