Income Statements - USD ($)	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Income Statement [Abstract]
Net Sales - from contracts with customers	$ 14,126,000	$ 11,931,000
Less: Cost of Goods Sold	(7,326,000)	(6,316,000)
Gross Profit	6,800,000	5,615,000
Operating Expenses:
General and Administrative	1,235,000	1,127,000
Sales	2,167,000	1,888,000
Engineering	74,000	90,000
Rent Paid to Related Parties	18,000	18,000
Total Operating Expenses	3,494,000	3,123,000
Income From Operations	3,306,000	2,492,000
Other Income (Expense)
Other	11,000	(112,000)
Interest Expense	(1,000)
Dividend and Interest Income	981,000	960,000
Unrealized Gain (Loss) on Equity Securities	444,000
Gain (Loss) on Sale of Investment	61,000	200,000
Gain (Loss) on Sale of Assets	(10,000)	6,000
Total Other Income	1,486,000	1,054,000
Income Before Provisions for Income Taxes	4,792,000	3,546,000
Provisions for Income Taxes
Current Expense	1,024,000	972,000
Deferred tax (benefit) expense	170,000	28,000
Total Income Tax Expense	1,194,000	1,000,000
Net Income	$ 3,598,000	$ 2,546,000
Earnings Per Share of Common Stock
Basic	$ 0.73	$ 0.51
Diluted	$ 0.72	$ 0.51
Weighted Average Number of Common Shares Outstanding (Basic)	3,598,000	4,958,769
Weighted Average Number of Common Shares Outstanding (Diluted)	4,983,047	4,977,584