Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Trade receivables, allowances	$ 112,000	$ 53,000
Intangible assets, accumulated amortization	$ 155,908	$ 149,740
Preferred stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred stock, authorized (in shares)	250,000	250,000
Preferred stock, issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	4,750,000	4,750,000
Common stock, share issued (in shares)	1,983,553	1,983,553
Common stock, share outstanding (in shares)	1,983,553	1,983,553