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Note 2 - Significant Accounting Policies (Details Textual) - USD ($)
3 Months Ended 6 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Cash, Uninsured Amount $ 1,298,000   $ 1,298,000  
Contract with Customer, Liability, Revenue Recognized $ 0   $ 120,000  
Earnings Per Share, Basic and Diluted, Total $ 0 $ 0 $ 0 $ 0
Maximum [Member]        
Product Warranty Expense $ 2,000 $ 2,000 $ 2,000 $ 2,000
Electronic Products [Member]        
Warranty Term     90 days