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Note 7 - Agreements, Commitments and Contingencies - Changes in Warranty Obligations (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Balance $ 813,288 $ 432,225
Warranty costs charged to cost of goods sold 348,241 707,079
Utilization charges against reserve (199,624) (315,556)
Release of accrual related to expired warranties 0 0
Foreign currency effect 94,708 (10,460)
Balance $ 1,056,613 $ 813,288