Inventories - Summary of inventories (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Inventories
Raw material and common parts	$ 15,771,000	$ 15,952,000
Work-in-process	4,181,000	3,432,000
Finished goods	2,144,000	2,490,000
Inventory, Gross	22,096,000	21,874,000
Less inventory reserve	(1,910,000)	(1,742,000)
Total inventories	$ 20,186,000	$ 20,132,000

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Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

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Gross amount, as of the balance sheet date, of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

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