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Note 6 - Agreements and Commitments (Tables)
 3 Months Ended
Mar. 31, 2019
Notes Tables  
Schedule of Product Warranty Liability [Table Text Block]
   
2019
  
Balance at December 31, 2018
   $
432,225
  
Current year warranty expense
    
313,894
  
Change in estimate related to pre-existing warranties
  
 
-
  
Payments made
    
-
  
Foreign currency effect
    
(11,588
)
Balance at March 31, 2019
   $
734,531