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Condensed Consolidated Statements of Cash Flows - USD ($)
 6 Months Ended
Nov. 30, 2018
Nov. 30, 2017
Operating activities:    
Net income $ 1,116,349 $ 353,894
Adjustments to reconcile net income to net cash flows from operating activities:    
Depreciation 555,967 507,179
Stock options issued for services 57,308 56,497
Changes in other assets and liabilities:    
Accounts receivable 1,271,944 (963,212)
Inventory 352,476 (265,192)
Costs and estimated earnings in excess of billings 77,048 (650,718)
Other current assets (34,718) 118,519
Accounts payable 659,370 11,605
Accrued commissions (13,612) 258,473
Billings in excess of costs and estimated earnings (1,224,319) (502,917)
Other current liabilities (388,793) 87,423
Net operating activities 2,429,020 (988,449)
Investing activities:    
Acquisition of property and equipment (325,754) (736,843)
Other investing activities (11,547) (10,937)
Net investing activities (337,301) (747,780)
Financing activities:    
Proceeds from issuance of common stock, net 14,334 124,621
Net change in cash and cash equivalents 2,106,053 (1,611,608)
Cash and cash equivalents - beginning 2,858,323 3,324,934
Cash and cash equivalents - ending $ 4,964,376 $ 1,713,326