Condensed Income Statements (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Income Statement [Abstract]
Net Sales	$ 3,455,000	$ 3,260,000	$ 10,551,000	$ 8,597,000
Less: Cost of Goods Sold	(1,772,000)	(1,826,000)	(5,467,000)	(4,337,000)
Gross Profit	1,683,000	1,434,000	5,084,000	4,260,000
Operating Expenses
General and Administrative	294,000	313,000	911,000	833,000
Sales	531,000	512,000	1,611,000	1,371,000
Engineering	21,000	22,000	57,000	69,000
Rent Paid to Related Parties	5,000	5,000	14,000	14,000
Total Operating Expenses	851,000	852,000	2,593,000	2,287,000
Income From Operations	832,000	582,000	2,491,000	1,973,000
Other Income
Other	1,000		10,000	3,000
Dividend and Interest Income	471,000	376,000	816,000	811,000
Gain on Investments	169,000	123,000	74,000	94,000
Gain on Sale of Assets				4,000
Total Other Income	641,000	499,000	900,000	912,000
Income Before Provisions for Income Taxes	1,473,000	1,081,000	3,391,000	2,885,000
Provisions for Income Taxes:
Current Expense	291,000	281,000	799,000	852,000
Deferred Tax Expense	9,000	9,000	33,000	1,000
Total Income Tax Expense	300,000	290,000	832,000	853,000
Net Income	1,173,000	791,000	2,559,000	2,032,000
Cash Dividends Common Stock			$ 1,886,000	$ 1,780,000
Income Per Share of Common Stock Basic	$ 0.24	$ 0.16	$ 0.52	$ 0.41
Income Per Share of Common Stock Diluted	$ 0.24	$ 0.16	$ 0.51	$ 0.41
Weighted Average Number of Common Shares Outstanding Basic	4,961,018	4,969,013	4,963,592	4,955,725
Weighted Average Number of Common Shares Outstanding Diluted	4,981,518	4,989,513	4,984,092	4,976,225