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Note 8 - Commitments and Contingencies (Tables)
6 Months Ended
Jun. 30, 2021
Notes Tables  
Schedule of Product Warranty Liability [Table Text Block]

Balance at December 31, 2020

  $ 154,000  

Warranties issued during the period

    21,000  

Settlements made during the period

    (75,000 )

Changes in liability for pre-existing warranties during the period

    --  

Balance at June 30, 2021

  $ 100,000