Cost of sales (Details) - EUR (€) € in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cost of sales
Personnel expenses	€ (4,594)	€ (5,583)	€ (5,404)
Material costs	(6,559)	(6,796)	(7,082)
Depreciation	(2,158)	(2,686)	(2,197)
Other expenses	(1,502)	(2,382)	(2,598)
Allowance for slow-moving inventory	1	21	417
Total	(14,812)	(17,426)	(16,864)
Cost of maintenance	208	535
Travel expense	171	312	294
Insurance expense	283	269
Rental and building expenses	104	149	491
License fees	€ 53	€ 57	€ 92

The amount of costs relating to expenses directly or indirectly attributed to the goods or services sold, which may include, but are not limited to, costs previously included in the measurement of inventory that has now been sold, unallocated production overheads and abnormal amounts of production costs of inventories.

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- Definition

The amount of depreciation expense. Depreciation is the systematic allocation of depreciable amounts of tangible assets over their useful lives.

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The amount of expense arising from purchased insurance.

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- Definition

The amount of expenses that the entity does not separately disclose in the same statement or note when the entity uses the 'nature of expense' form for its analysis of expenses. [Refer: Expenses, by nature]

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The amount of raw materials and consumables used in the production process or in the rendering of services. [Refer: Current raw materials]

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The amount of expense recognised on rental activities.

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The amount of expenses incurred for the day-to-day servicing of assets, which may include the cost of labour, consumables or small parts.

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The amount of expense from employee benefits (other than termination benefits) that are expected to be settled wholly within twelve months after the end of the annual reporting period in which the employees render the related services.

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The amount of expense arising from travel.

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The amount recognised resulting from the write-down of inventories to net realisable value or reversals of those write-downs. [Refer: Inventories]

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The amount of fees paid or payable for licenses.

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