Condensed Consolidated Statements of Cash Flow - USD ($)	6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016
Operating activities:
Net income	$ 353,894	$ 1,148,114
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	507,179	453,823
Stock options issued for services	56,497	78,789
Changes in other assets and liabilities:
Accounts receivable	(963,212)	208,765
Inventory	(265,192)	(884,013)
Costs and estimated earnings in excess of billings	(650,718)	(923,853)
Other current assets	118,519	164,341
Accounts payable	11,605	274,686
Accrued commissions	258,473	214,972
Billings in excess of costs and estimated earnings	(502,917)	(625,204)
Other current liabilities	87,423	(1,077,518)
Net operating activities	(988,449)	(967,098)
Investing activities:
Acquisition of property and equipment	(736,843)	(1,237,072)
Other investing activities	(10,937)	(17,024)
Net investing activities	(747,780)	(1,254,096)
Financing activities:
Proceeds from issuance of common stock, net	124,621	150,940
Net change in cash and cash equivalents	(1,611,608)	(2,070,254)
Cash and cash equivalents - beginning	3,324,934	6,086,080
Cash and cash equivalents - ending	$ 1,713,326	$ 4,015,826