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Note 1 - Significant Accounting Policies - Summaries of Allowance for Doubtful Accounts (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Balance $ 8,000 $ 8,000
Additions charged to expense
Recovery of amounts previously reserved
Amounts written off
Balance at end of year $ 8,000 $ 8,000