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

June 30,

2021

   

December 31,

2020

 

Balance at January 1

  $ 1,056,613     $ 813,288  

Warranty costs charged to cost of goods sold

    51,552       348,241  

Utilization charges against reserve

    (102,455

)

    (199,624

)

Release of accrual related to expired warranties

    -       -  

Foreign currency effect

    (33,015

)

    94,708  

Balance at the end of the period

  $ 972,695     $ 1,056,613