Note 2 - Income Taxes - Net Deferred Tax Liabilities (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities:
Accrued vacation	$ 33,000	$ 21,000
Inventories reserve	17,000	42,000
Allowance for doubtful accounts	2,000	3,000
Allowance for sales returns	10,000	10,000
Research and development credit carryforward	285,000	245,000
Accrued self-insured medical		3,000
Property and equipment	(257,000)	(295,000)
Patents	(50,000)	(53,000)
Net operating loss	411,000	230,000
Other	17,000	8,000
Valuation allowance	(468,000)	(214,000)
Net deferred tax liabilities

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from inventory.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from employee benefits, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the allowance for doubtful accounts.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from estimated returns and sales allowances.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from estimated losses under self insurance.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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