LEASES - Supplemental components of cash flow (Details) - USD ($)	3 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Apr. 30, 2020
LEASES
Operating cash flows from operating leases	$ 109,000	$ 112,000
Financing cash flows from finance leases	15,000	16,000
Total cash paid for amounts included in the measurement of leases	$ 124,000	$ 128,000
Weighted average remaining lease term, operating leases	6 years 2 months 1 day		6 years 7 months 6 days
Weighted average remaining lease term, finance leases	3 months		5 months 1 day
Weighted average discount rate, operating leases	4.52%		4.52%
Weighted average discount rate, finance leases	5.44%		5.43%