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Note 3 - Significant Accounting Policies - Reserve for Product Warranty Activity (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Balance, beginning of the period $ 153,723 $ 40,000
Provision for product warranty
Product warranty expirations
Product warranty costs paid (6,773)
Balance, end of the period $ 146,950 $ 40,000