Note 6 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)	Mar. 31, 2019	Mar. 31, 2018
Paid time off accrual	$ 55,900	$ 59,171
Inventory reserve	41,572	41,572
Depreciation and amortization	112,125	81,385
Stock-based compensation deductions	62,671	55,886
Unrealized loss on marketable securities	23,170	273,360
Other	58,297	61,281
Deferred tax assets	$ 353,735	$ 572,655