Note 6 - Inventories (Tables)
 9 Months Ended
Dec. 31, 2018
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
December 31,
2018
    
March 31,
2018
  
Raw materials
   $
1,155,148
     $
1,084,030
  
Work in process
    
2,265,585
      
1,828,492
  
Finished goods
    
720,748
      
737,917
  
Total inventories
   $
4,141,481
     $
3,650,439