Note 2 - Income Taxes - Net Deferred Tax Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred tax liabilities:
Accrued vacation	$ 18,000	$ 19,000
Inventories reserve	46,000	46,000
Allowance for doubtful accounts	2,000	2,000
Allowance for sales returns	9,000	9,000
Research and development credit carryforward	161,000	131,000
Accrued self-insured medical	4,000	1,000
Property and equipment	(282,000)	(242,000)
Intangible assets	(73,000)	(65,000)
Net operating loss	33,000	40,000
Other	8,000	6,000
Valuation allowance	(109,000)	(91,000)
Net deferred tax liabilities	$ (183,000)	$ (144,000)