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6. Inventories (Details) - USD ($)
$ in Millions
Apr. 30, 2019
Apr. 30, 2018
Frequency Electronics Inc Zyfer [Member]    
6. Inventories (Details) [Line Items]    
Inventory Adjustments $ 1.1 $ 5.6
Frequency Electronics Inc New York [Member]    
6. Inventories (Details) [Line Items]    
Inventory, Work in Process, Net of Reserves $ 6.6 $ 5.5