Revenue Recognition Our revenue is generated primarily from the sale of products and services. Product revenue primarily consists of sales of our instruments and related consumables; service and other revenue primarily consists of revenue earned from product maintenance agreements with some additional revenue from instrument lease agreements and grant revenue. We account for a contract with a customer when there is a legally enforceable contract between us and the customer, the rights of the parties are identified, the contract has commercial substance, and collectability of the contract consideration is probable. Revenues are recognized when control of the promised goods or services is transferred to our customers or services are performed, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Taxes we collect concurrent with revenue-producing activities are excluded from revenue. Our instrument sales are generally sold in a bundled arrangement and commonly include the instrument, instrument accessories, installation, training, and consumables. Additionally, our instrument sale arrangements generally include a one-year period of service. For such bundled arrangements, we account for individual products and services separately if they are distinct, that is, if a product or service is separately identifiable from other items in the bundled package and if a customer can benefit from it on its own or with other resources that are readily available to the customer. Our customers cannot benefit from our instrument systems without installation, and installation can only be performed by us or qualified distributors. As a result, the system and installation are considered to be a single performance obligation recognized after installation is completed except for sales to qualified distributors, in which case the system is distinct and recognized when control has transferred to the distributor which typically occurs upon shipment. The consideration for bundled arrangements is allocated between separate performance obligations based on their individual standalone selling price (SSP). The SSP is determined based on observable prices at which we separately sell the products and services. If a SSP is not directly observable, then we will estimate the SSP by considering multiple factors including, but not limited to, overall market conditions, including geographic or regional specific factors, internal costs, profit objectives, pricing practices and other observable inputs. We recognize revenues as performance obligations are satisfied by transferring control of the product or service to the customer or over the term of a product maintenance agreement with a customer. Our revenue arrangements generally do not provide a right of return. Contract liabilities and contract assets - Contract liabilities consist of deferred revenue. We record deferred revenues when cash payments are received or due in advance of our performance for product maintenance agreements. Deferred revenue is recognized over the related performance period, generally one to three years, on a straight-line basis as we are standing ready to provide services and a time-based measure of progress best reflects the satisfaction of the performance obligation. As of December 31, 2019, we had a total of $0.6 million of deferred commissions included in Prepaid expenses and other current assets which is recognized as the related revenue is recognized. Additionally, as a practical expedient, we expense costs to obtain a contract as such costs are incurred if the amortization period would have been a year or less. Contract assets as of December 31, 2019 and December 31, 2018 were not material. Instrument lease agreements - Instrument leases are generally classified as operating-type leases and revenue from these leases is recognized on a straight-line basis over the respective lease term, once the lessee takes (or has the right to take) control/possession of the property under the lease. Effectively, this occurs once the installation is complete and control of the instrument is transferred to our customers. Other practical expedients and exemptions - Customers generally are invoiced upon acceptance of the system, which is also the start of the one -year service period. As such, there is typically not more than a one-year difference between the receipt of cash and the provision of services. Therefore, we apply the practical expedient and do not account for any potential significant financing benefit. However, it is noted that some customers will pre-order extended service periods at the time of the initial system sale. These customers may choose to make quarterly or annual payments or prepay multiple years of service upfront but there is no pricing difference between these different payment options. As such, no significant financing component is believed to exist with any of our existing arrangements.