Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 510,922	$ 647,057
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation	303,197	299,355
Gain from disposal of equipment	(400)	(1,022)
Deferred income taxes	(17,000)	(8,000)
Changes in operating assets and liabilities:
Accounts receivable	(850,265)	(673,585)
Inventories	(749,749)	(381,492)
Other current assets	89,318	270,617
Accounts payable	646,777	649,419
Accrued wages and salaries	(5,357)	22,441
Other accrued expenses	(127,111)	(128,290)
Unearned revenue and customer deposits	59,162	(19,000)
Net cash provided by (used in) operating activities	(140,506)	677,500
Cash flows from investing activities:
Capital expenditures	(175,462)	(596,831)
Proceeds from the sale of equipment	400	1,022
Proceeds from certificates of deposit	1,992,000	1,494,000
Purchases of certificates of deposit	(747,000)	(996,000)
Net cash provided by (used in) investing activities	1,069,938	(97,809)
Cash flows from financing activities:
Cash dividends paid	(531,373)	(415,437)
Net cash used in financing activities	(531,373)	(415,437)
Net increase (decrease) in cash and cash equivalents	398,059	164,254
Cash and cash equivalents at beginning of period	353,475	800,894
Cash and cash equivalents at end of period	751,534	965,148
Supplemental schedule of non-cash investing activities:
Capital expenditures in accounts payable	$ 1,852	$ 2,550