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Note 6 - Share Based Compensation (Tables)
3 Months Ended
Mar. 31, 2021
Notes Tables  
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
   
Three Months Ended March 31,
 
   
2021
   
2020
 
                 
                 
Selling, general and administrative
  $
128,944
    $
441,308
 
Research, development and engineering
   
12,204
     
71,411
 
    $
141,148
    $
512,719