Note 2 - Income Taxes - Net Deferred Tax Liabilities (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Deferred tax liabilities:
Accrued vacation	$ 21,000	$ 18,000
Inventories reserve	42,000	46,000
Allowance for doubtful accounts	3,000	2,000
Allowance for sales returns	10,000	9,000
Research and development credit carryforward	245,000	161,000
Accrued self-insured medical	3,000	4,000
Property and equipment	(295,000)	(282,000)
Intangible assets	(53,000)	(73,000)
Net operating loss	230,000	33,000
Other	8,000	8,000
Valuation allowance	(214,000)	(109,000)
Net deferred tax liabilities		$ (183,000)