Balance Sheets (Parentheticals) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Allowance for doubtful accounts	$ 61,376	$ 77,623
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares issued (in shares)	4,656,734	4,656,734
Common stock, shares outstanding (in shares)	4,521,988	4,506,788
Treasury stock, shares (in shares)	134,746	149,946