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Note 8 - Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2019
Notes Tables  
Schedule of Product Warranty Liability [Table Text Block]
   
Year Ended December 31,
  
   
2019
    
2018
  
Beginning balance
   $
186,000
     $
291,000
  
Warranties originated during the year
    
254,000
      
199,000
  
Claims settled made during the year
    
(154,000
 )    
(252,000
 )
Changes in reserve estimate
    
(9,000
 )    
(52,000
 )
Ending balance
   $
277,000
     $
186,000