Note 9 - Share-based Compensation - Summary of Option Activity Under Stock Plans (Details) - USD ($)	6 Months Ended	12 Months Ended
	Sep. 30, 2022	Mar. 31, 2022
Outstanding (in shares)	252,500
Outstanding, weighted average exercise price (in dollars per share)	$ 3.34
Outstanding, weighted average remaining contractual term (Year)	8 years	6 years 6 months
Outstanding, aggregate intrinsic value	$ 250	$ 159,650
Granted (in shares)	50,000
Granted, weighted average exercise price (in dollars per share)	$ 3.43
Expired (in shares)	(49,500)
Expired, weighted average exercise price (in dollars per share)	$ 5.80
Outstanding (in shares)	253,000	252,500
Outstanding, weighted average exercise price (in dollars per share)	$ 2.88	$ 3.34
Exercisable (in shares)	111,333
Exercisable, weighted average exercise price (in dollars per share)	$ 2.90
Exercisable, weighted average remaining contractual term (Year)	7 years 1 month 6 days
Exercisable, aggregate intrinsic value	$ 250