Deferred Revenue

6 Months Ended

Jun. 30, 2022

Deferred Revenue Disclosure [Abstract]

Deferred Revenue

Note 10. Deferred Revenue

Deferred revenue, comprising individually immaterial amounts for extended warranty, enhanced maintenance and advance payments on non-recurring engineering services contracts, represents contracted revenue that has not yet been recognized. Deferred revenue as of December 31, 2020, included a $6.0 million advance payment for a system order, which we recognized as revenue in first-half 2021. We recognized $270,000 of revenue related to amounts included in deferred revenue as of December 31, 2021 for the six months ended June 30, 2022. We recognized $6.6 million of revenue related to amounts included in deferred revenue as of December 31, 2020 for the six months ended June 30, 2021.

The following table presents the changes in deferred revenue for the periods presented (in thousands):

	Six Months Ended June 30,
	2022			2021
Balance at beginning of period	$	794		$	7,088
Deferral of revenue		2,661			319
Recognition of deferred revenue		(459	)		(6,872	)
Balance at end of period	$	2,996		$	535