Note 4 - Basic and Diluted Earnings (Loss) Per Share - Basic and Diluted Earnings (Loss) Per Share (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income (loss)	$ (388,105)	$ 623,644	$ (977,954)	$ (238,305)	$ 235,539	$ (1,216,259)
Denominator for basic earnings (loss) per share – weighted average shares (in shares)	1,746,000		1,845,000		1,746,000	1,845,000
Dilutive effect of employee stock options and other warrants (in shares)
Denominator for diluted earnings (loss) per share – adjusted weighted average shares (in shares)	1,746,000		1,845,000		1,746,000	1,845,000
Basic earnings (loss) per share (in dollars per share)	$ (0.22)		$ (0.53)		$ 0.13	$ (0.66)
Diluted earnings (loss) per share (in dollars per share)	$ (0.22)		$ (0.53)		$ 0.13	$ (0.66)