Condensed Income Statements (Unaudited) - USD ($)	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Income Statement [Abstract]
Net Sales	$ 2,248,000	$ 2,666,000
Less: Cost of Goods Sold	(1,095,000)	(1,386,000)
Gross Profit	1,153,000	1,280,000
Operating Expenses:
General and Administrative	229,000	211,000
Sales	416,000	484,000
Engineering	13,000	18,000
Rent Paid to Related Parties	5,000	5,000
Total Operating Expenses	663,000	718,000
Income From Operations	490,000	562,000
Other Income (Expense)
Other	3,000	3,000
Dividend and Interest Income	279,000	192,000
Gain (Loss) on Sales of Assets	4,000
Gain (Loss) on Sale of Investments	(38,000)	47,000
Total Other Income (Expense)	248,000	242,000
Income Before Provisions for Income Taxes	738,000	804,000
Provisions for Income Taxes
Current Expense	213,000	258,000
Deferred tax expense (benefit)	7,000	(21,000)
Total Income Tax Expense	220,000	237,000
Net Income	$ 518,000	$ 567,000
Basic Earnings Per Share of Common Stock	$ 0.10	$ 0.11
Diluted Earnings Per Share of Common Stock	$ 0.10	$ 0.11
Weighted Average Number of Common Shares Outstanding	4,945,092	5,021,727
Weighted Average Number of Shares Outstanding (Diluted)	4,965,592	5,042,227