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BALANCE SHEETS (Parenthetical) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Accounts receivable, allowance for doubtful accounts (in dollars) $ 146,832 $ 149,665
Common stock, par value (in dollars per share) $ 0 $ 0
Common Stock, authorized shares 100,000,000 100,000,000
Common Stock, outstanding shares 32,674,954 32,666,454
Preferred Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, Shares Authorized 5,000,000 5,000,000
Series I, Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, outstanding shares 96,000 98,500
Preferred Stock, liquidation preference (in dollars) $ 600,000  
Common Stock, outstanding shares   98,500
Series II, Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, outstanding shares 171,200 171,200
Preferred Stock, liquidation preference (in dollars) $ 2,140,000  
Series III, Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, outstanding shares 129,245 129,245
Preferred Stock, liquidation preference (in dollars) $ 1,615,563  
Series IV, Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, outstanding shares 342,500 342,500
Preferred Stock, liquidation preference (in dollars) $ 3,767,500  
Series V, Class B    
Preferred stock, par value (in dollars per share) $ 1 $ 1
Preferred Stock, outstanding shares 34,000 40,000
Preferred Stock, liquidation preference (in dollars) $ 149,600