Annual report pursuant to Section 13 and 15(d)

BALANCE SHEETS (Parenthetical)

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BALANCE SHEETS (Parenthetical) - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Statement of Financial Position [Abstract]    
Accounts receivable, allowance for doubtful accounts $ 37,500 $ 77,067
Patents, accumulated amortization $ 239,581 $ 203,768
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, authorized 75,000,000 75,000,000
Common stock, issued 40,932,911 40,731,529
Common stock, outstanding 38,195,680 37,994,298
Treasury stock 2,737,231 2,737,231