Balance sheet detail as of March 31, 2022 and December 31, 2021 is as follows (in thousands):

Inventories


	March 31, 2022 (As Restated)		December 31, 2021
Raw materials	$	45,527	$	34,512
Work in process		1,216		1,427
Finished goods		23,342		20,954
Total inventories	$	70,085	$	56,893

Inventories are stated at the lower of cost or net realizable value, with cost being computed based on an adjusted standard basis, which approximates actual cost on an average or first-in, first-out basis. Finished goods include deferred cost of revenue of $4.3 million and $0.7 million as of March 31, 2022 and December 31, 2021, respectively.

Provision for inventory write-down was $0.7 million as of March 31, 2022 and March 31, 2021 each.

Property, plant and equipment


	March 31, 2022			December 31, 2021
Property, plant and equipment, net:
Machinery and equipment	$	17,090		$	14,278
Leasehold improvements		5,251			5,219
Computers and software		3,278			3,217
Furniture and fixtures		1,726			1,771
Construction in progress and other		1,052			2,937
		28,397			27,422
Less: accumulated depreciation and amortization		(17,971	)		(17,394	)
Less: government grants		(149	)		(186	)
Total property, plant and equipment, net	$	10,277		$	9,842

Depreciation expense associated with property, plant and equipment was $0.8 million and $0.9 million for the three months ended March 31, 2022 and 2021, respectively.

The Company receives grants from certain foreign government entities mainly to support capital expenditures in the region. Such grants are deferred and are generally refundable to the extent the Company does not utilize the funds for qualifying expenditures. Once earned, the Company records the grants as a contra amount to the assets and amortizes such amount over the useful lives of the related assets as a reduction to depreciation expense.

The Company accrues warranty costs based on historical trends for the expected material and labor costs to provide warranty services. The Company's standard warranty period is one year from the date of shipment with the ability for customers to purchase an extended warranty of up to five years from the date of shipment. The following table summarizes the activity related to the product warranty liability:


	Three Months Ended March 31,
	2022			2021
Balance at beginning of period	$	1,981		$	1,522
Charged to cost of revenue		121			269
Claims and settlements		(149	)		(267	)
Foreign currency exchange impact		(17	)		56
Balance at end of period	$	1,936		$	1,580

The Company records contract assets when it has a right to consideration and records accounts receivable when it has an unconditional right to consideration. Contract liabilities consist of cash payments received (or unconditional rights to receive cash) in advance of fulfilling performance obligations. The majority of the Company's performance obligations in its contracts with customers relate to contracts with duration of less than one year.

The opening and closing balances of current and long-term contract assets and contract liabilities related to contracts with customers are as follows:


	Contract assets			Contract liabilities
December 31, 2021	$	2,184		$	9,135
March 31, 2022 (As Restated)		902			11,387
Increase (decrease) (As Restated)	$	(1,282	)	$	2,252

The decrease in contract assets during the three months ended March 31, 2022 was primarily due to invoicing that occurred in 2022 from unbilled balances reflected as contract assets as of December 31, 2021.

The increase in contract liabilities during the three months ended March 31, 2022 was primarily due to amounts being invoiced for certain customers that have not yet met the revenue recognition criteria. The amount of revenue recognized in the three months ended March 31, 2022 that was included in the prior period contract liability balance was $2.4 million. The amount of revenue recognized in the three months ended March 31, 2021 that was included in the prior period contract liability balance was $2.1 million. This revenue consists of services provided to customers who had been invoiced prior to the current year. We expect to recognize approximately 75%of outstanding contract liabilities as revenue over the next 12 months and the remainder thereafter.

The balance of contract cost deferred as of March 31, 2022 and December 31, 2021 was $0.6 million and $0.8 million, respectively. During the three months ended March 31, 2022 the Company recorded $0.2 million in amortization related to contract cost deferred as of December 31, 2021. During the three months ended March 31, 2021 the Company recorded $0.4 million in amortization related to contract cost deferred as of December 31, 2020.