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Inventories (Tables)
3 Months Ended
Mar. 31, 2019
Inventory Disclosure [Abstract]  
Inventory components

Inventories consist principally of raw materials and sub-assemblies, which are stated at the lower of cost (first-in, first-out) or market. Inventories at March 31, 2019 and December 31, 2018 were as follows:

 

   March 31,  December 31,
   2019  2018
Raw materials and sub-assemblies  $3,189,762   $2,785,154 
Finished goods   154,024    335,335 
Inventory reserves   (848,161)   (848,161)
Inventory, net  $2,495,625  $2,272,328