11. Investment in Morion, Inc. (Details) - USD ($)		1 Months Ended	12 Months Ended
	Oct. 22, 2012	Nov. 30, 2012	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016	Mar. 29, 2016
11. Investment in Morion, Inc. (Details) [Line Items]
Revenue from Related Parties			$ 2,000	$ 203,000
Morion Inc [Member]
11. Investment in Morion, Inc. (Details) [Line Items]
Cost Method Investment Ownership Percentage			4.60%
Investment Owned, at Cost			$ 800,000
Related Party Transaction, Purchases from Related Party			437,000	446,000
Revenue from Related Parties		$ 375,000	2,000	203,000
Accounts Receivable, Related Parties, Current			38,000
Accounts Payable, Related Parties, Current				85,000
Proceeds from Dividends Received			$ 105,000	$ 85,000
Morion Inc [Member] | Licensing Agreement [Member]
11. Investment in Morion, Inc. (Details) [Line Items]
Revenue from Related Parties					$ 210,000
Long-term Purchase Commitment, Description	The agreement required the Company to sell certain fully-depreciated production equipment previously owned by the Company and to provide training to Morion employees to enable Morion to produce a minimum of 5,000 rubidium oscillators per year.
License And Equipment Fee Receivable	$ 2,700,000						$ 602,000
Percentage Of Royalties Payable On Third Party Sales	5.00%
Long-term Purchase Commitment, Period	5 years
Purchase Commitment, Remaining Minimum Amount Committed	$ 400,000
Revenue from Contract with Customer, Including Assessed Tax						$ 392,500