Note 6 - Inventories (Tables)
 3 Months Ended
Jun. 30, 2020
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
June 30,
2020
    
March 31,
2020
  
Raw materials
   $
907,618
     $
1,017,451
  
Work in process
    
2,026,032
      
1,863,000
  
Finished goods
    
1,010,088
      
1,003,999
  
Total inventories
   $
3,943,738
     $
3,884,450