Payment terms typically require payment upon shipment or installation of the System and additional payments as access codes for Treatment Sessions are delivered, which can span several years after the System is first delivered and installed. The timing of revenue recognition compared to billings and cash collections typically results in accounts receivable. However, sometimes customer advances and deposits might be required for certain customers and are recorded as deferred revenue. For multi-year agreements, the Company generally invoices customers annually at the beginning of each annual coverage period and recognizes revenue over the term of the coverage period.

As of March 31, 2020, the Company expects to recognize approximately the following percentages of deferred revenue by year:

Year:	Revenue Recognition
2020		45	%
2021		16	%
2022		12	%
2023		12	%
2024		11	%
Thereafter		4	%
Total		100	%

Revenue recognized for the three months ended March 31, 2020 that was included in the contract liability balance at the beginning of the year was $0.9 million, and primarily represented revenue earned from separately priced extended warranties, rent-to-own revenue, milestone revenue, and clinical training.

For the three months ended March 31, 2020 one customer accounted for more than 10% of the Company’s revenues. No customer accounted for more than 10% of the Company’s revenues for the same period in 2019.