Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 707,788	$ 510,922
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation	326,520	303,197
Gain from disposal of equipment	(300)	(400)
Deferred income taxes	(14,000)	(17,000)
Changes in operating assets and liabilities:
Accounts receivable	(1,427,855)	(850,265)
Inventories	(68,578)	(749,749)
Other current assets and prepaid income taxes	102,899	89,318
Accounts payable	908,830	646,777
Accrued wages and salaries	(14,635)	(5,357)
Other accrued expenses	(67,446)	(127,111)
Unearned revenue and customer deposits	(238,722)	59,162
Net cash provided by (used in) operating activities	214,501	(140,506)
Cash flows from investing activities:
Capital expenditures	(225,000)	(175,462)
Proceeds from the sale of equipment	300	400
Proceeds from certificates of deposit	1,494,000	1,992,000
Purchases of certificates of deposit	(1,245,000)	(747,000)
Net cash provided by investing activities	24,300	1,069,938
Cash flows from financing activities:
Cash dividends paid	(492,727)	(531,373)
Net cash used in financing activities	(492,727)	(531,373)
Net (decrease) increase in cash and cash equivalents	(253,926)	398,059
Cash and cash equivalents at beginning of period	1,152,569	353,475
Cash and cash equivalents at end of period	898,643	751,534
Supplemental schedule of non-cash investing activities:
Capital expenditures in accounts payable	$ 1,427	$ 1,852