Note 6 - Inventories (Tables)
 6 Months Ended
Sep. 30, 2020
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
Sept. 30,
2020
    
March 31,
2020
  
Raw materials
   $
953,050
     $
1,017,451
  
Work in process
    
1,949,981
      
1,863,000
  
Finished goods
    
1,025,493
      
1,003,999
  
Total inventories
   $
3,928,524
     $
3,884,450