Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 1,045	$ 1,090
Investments	8,042	8,041
Trade receivables, less allowance for doubtful accounts of $11	1,209	957
Inventories	1,568	1,572
Other current assets	206	170
Income tax receivable	19	26
Total current assets	12,089	11,856
Deferred income tax asset, net	253	246
Intangible assets, net	163	228
Property and equipment, net	964	989
Total assets	13,469	13,319
Current liabilities
Current maturities of financing lease	6	6
Accounts payable	190	197
Accrued expenses	489	330
Total current liabilities	685	533
Long-term liabilities
Financing lease, net of current maturities	11	12
Total long-term liabilities	11	12
Commitments and contingencies
Stockholders' equity
Common stock par value $0.10 per share; authorized 10,000,000 shares; 3,395,521 shares issued and outstanding	339	339
Additional paid-in capital	2,037	2,036
Retained earnings	10,396	10,398
Accumulated other comprehensive gain (unrealized gain on available-for-sale securities, net of income tax)	1	1
Total stockholders' equity	12,773	12,774
Total liabilities and stockholders' equity	$ 13,469	$ 13,319