Note 7 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)	Mar. 31, 2018	Mar. 31, 2017
Paid time off accrual	$ 59,171	$ 109,298
Inventory reserve	41,572	81,743
Depreciation and amortization	81,385	52,378
Stock-based compensation deductions	55,886	86,335
Unrealized loss on marketable securities	273,360	21,852
Other	61,281	5,449
Deferred tax assets	$ 572,655	$ 357,055