Income Statements - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016
Income Statement [Abstract]
Net Sales	$ 10,904,000	$ 11,240,000
Less: Cost of Goods Sold	(5,224,000)	(4,977,000)
Gross Profit	5,680,000	6,263,000
Operating Expenses:
General and Administrative	914,000	853,000
Sales	1,892,000	1,937,000
Engineering	73,000	92,000
Rent Paid to Related Parties	18,000	19,000
Total Operating Expenses	2,897,000	2,901,000
Income From Operations	2,783,000	3,362,000
Other Income (Expense)
Other Income	11,000	16,000
Dividend and Interest Income	774,000	867,000
Gain (Loss) on Investments	(40,000)	72,000
Total Other Income (Expense)	745,000	955,000
Income Before Provisions for Income Taxes	3,528,000	4,317,000
Provisions for Income Taxes
Current Expense	1,140,000	1,252,000
Deferred tax (benefit) expense	(13,000)	(21,000)
Total Income Tax Expense	1,127,000	1,231,000
Net Income	$ 2,401,000	$ 3,086,000
Earnings Per Share of Common Stock
Basic	$ 0.48	$ 0.61
Diluted	$ 0.48	$ 0.61
Weighted Average Number of Common Shares Outstanding (Basic)	4,984,013	5,024,428
Weighted Average Number of Common Shares Outstanding (Diluted)	5,004,513	5,044,928