Note D - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Allowance for doubtful accounts	$ 4,447	$ 3,548
Inventories	7,350	4,200
Accounts payable	14,991	39,227
Accrued expenses	235,633	215,604
Total deferred tax assets	262,421	262,579
Deferred tax liabilities
Accounts receivable	(445,113)	(354,787)
Prepaid expenses	(42,319)	(38,913)
Depreciation on property, plant and equipment	(73,384)	(69,424)
Unrealized gain on marketable securities	(88,460)	(53,038)
Total deferred tax liabilities	(649,276)	(516,162)
Net deferred tax liability	$ (386,855)	$ (253,583)