Accounts receivable are recorded at invoiced amounts with standard net terms that range between 30 and 90 days. The Company extends credit to its customers based on an evaluation of a customer’s financial condition and collateral is generally not required. The Company maintains an allowance for estimated uncollectible accounts receivable. The allowance is based on the Company’s assessment of known delinquent accounts, historical experience, and other currently available evidence of the collectability and the aging of accounts receivable. The Company’s allowance for doubtful accounts was $0.1 million at March 31, 2019 and at December 31, 2018.

Inventories are stated at the lower of cost or market and include material, labor and overhead costs using the first-in, first-out method of costing. Inventories as of March 31, 2019 and December 31, 2018 were composed of raw materials, sub-assemblies, finished goods and work-in-process. The Company had consigned inventory with customers of $0.4 million and $0.9 million at March 31, 2019 and December 31, 2018, respectively. The Company records allowances to reduce the value of inventory to the lower of cost or market, including allowances for excess and obsolete inventory. Reserves for excess inventory are calculated based on our estimate of inventory in excess of normal and planned usage. Obsolete reserves are based on our identification of inventory where the carrying value is above net realizable value. The allowance for inventory losses was $3.3 million at March 31, 2019 and at December 31, 2018.

	March 31, 2019		December 31, 2018
Raw materials	$	6,862	$	7,023
Work-in-process		1,535		1,388
Finished goods		4,522		4,437
Inventories, net	$	12,919	$	12,848

Prepaid assets are stated at cost and are amortized over the useful lives (up to one year) of the assets.

Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets. The Company depreciates computer equipment over three to five years, office equipment, manufacturing and test equipment, and motor vehicles over five years, furniture and fixtures over seven years, and buildings over 30 years. Leasehold improvements are amortized over the shorter of the corresponding lease term or useful life. Depreciation expense and gains and losses on the disposal of property and equipment are included in cost of sales and operating expenses in the condensed consolidated statements of operations. Maintenance and repairs are expensed as incurred.

	March 31, 2019			December 31, 2018
Building	$	6,372		$	6,351
Computers and office equipment		10,649			10,963
Manufacturing and test equipment		13,886			13,573
Furniture and fixtures		1,319			1,318
Leasehold improvements		1,556			1,529
Motor vehicles		20			20
Total property and equipment		33,802			33,754
Less: Accumulated depreciation and amortization		(23,832	)		(23,386	)
Land		1,770			1,770
Property and equipment, net	$	11,740		$	12,138

Depreciation and amortization expense was approximately $0.7 million for the three months ended March 31, 2019 and 2018, respectively. Amortization for finance leases is included in depreciation and amortization expense. See Note 10 for information related to finance leases.

	March 31, 2019		December 31, 2018
Payroll, bonuses, and other employee benefits	$	1,406	$	1,409
Inventory receipts		1,356		1,396
Paid time off		985		936
Short-term obligations under operating leases		876		0
Warranties		384		339
Professional fees and contractors		290		346
Income and sales taxes		241		186
Real estate taxes		185		148
Employee stock purchase plan		143		343
Customer refunds for estimated returns		142		154
Deferred revenues		126		149
Short-term obligations under finance leases		80		91
Other		454		304
Total	$	6,668	$	5,801

	March 31, 2019		December 31, 2018
Finance leases	$	117	$	132
Operating leases		562		0
Deferred Rent		0		87
Other		189		162
Total	$	868	$	381