Condensed Income Statements (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021
Income Statement [Abstract]
Net Sales	$ 5,054,000	$ 4,633,000	$ 15,252,000	$ 13,327,000
Less: Cost of Goods Sold	(2,861,000)	(2,385,000)	(7,908,000)	(6,631,000)
Gross Profit	2,193,000	2,248,000	7,344,000	6,696,000
Operating Expenses
General and Administrative	371,000	362,000	1,070,000	1,040,000
Sales	649,000	639,000	2,109,000	1,809,000
Engineering	29,000	31,000	67,000	81,000
Total Operating Expenses	1,049,000	1,032,000	3,246,000	2,930,000
Income From Operations	1,144,000	1,216,000	4,098,000	3,766,000
Other Income (Expense)
Other	1,000	952,000	15,000	1,008,000
Dividend and Interest Income	552,000	317,000	876,000	608,000
Unrealized Gain (Loss) on equity securities	(1,729,000)	2,654,000	(687,000)	4,653,000
Gain on Sale of Investments	91,000	250,000	391,000	293,000
Gain on Sale of Assets				4,000
Total Other Income (Expense)	(1,085,000)	4,173,000	595,000	6,566,000
Income Before Provisions for Income Taxes	59,000	5,389,000	4,693,000	10,332,000
Provisions for Income Taxes:
Current Expense	455,000	199,000	1,407,000	1,230,000
Deferred Tax Expense (Benefit)	(557,000)	743,000	(309,000)	1,303,000
Total Income Tax Expense (Benefit)	(102,000)	942,000	1,098,000	2,533,000
Net Income	$ 161,000	$ 4,447,000	$ 3,595,000	$ 7,799,000
Income Per Share of Common Stock
Basic	$ 0.03	$ 0.90	$ 0.73	$ 1.58
Diluted	$ 0.03	$ 0.89	$ 0.72	$ 1.57
Weighted Average Number of Common Shares Outstanding
Basic	4,943,985	4,948,224	4,945,192	4,949,351
Diluted	4,964,485	4,968,724	4,965,692	4,969,851