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Note 2 - Revenue from Contracts with Customers - Changes in Contract Liabilities (Details) - USD ($)
3 Months Ended
Jun. 30, 2020
Mar. 31, 2020
Contract liabilities, balance $ 270,791 $ 464,223
Contract liabilities added 9,906 19,136
Revenue recognized (216,353) (212,568)
Contract liabilities, balance $ 64,344 $ 270,791