Note 10 - Share-based Compensation - Summary of Option Activity Under Stock Plans (Details) - USD ($)	9 Months Ended	12 Months Ended
	Dec. 31, 2021	Mar. 31, 2021
Outstanding (in shares)	374,300
Outstanding, weighted average exercise price (in dollars per share)	$ 3.64
Outstanding, weighted average remaining contractual term (Year)	6 years 8 months 12 days	3 years
Outstanding, aggregate intrinsic value	$ 135,600	$ 129,700
Granted (in shares)	50,000
Granted, weighted average exercise price (in dollars per share)	$ 2.96
Forfeited (in shares)	(3,000)
Forfeited, weighted average exercise price (in dollars per share)	$ 4.95
Expired (in shares)	(166,800)
Expired, weighted average exercise price (in dollars per share)	$ 3.84
Outstanding (in shares)	254,500	374,300
Outstanding, weighted average exercise price (in dollars per share)	$ 3.36	$ 3.64
Exercisable (in shares)	112,833
Exercisable, weighted average exercise price (in dollars per share)	$ 4.37
Exercisable, weighted average remaining contractual term (Year)	4 years 1 month 6 days
Exercisable, aggregate intrinsic value	$ 39,183