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English: Linen testers are small magnifiers with a built-in folding stand. They have a fixed focus and a wide field of view, arranged so that when placed on a flat surface, such a piece of cloth, this surface will be in focus. The base is usually calibrated as a ruler. Their name derives from their original use for counting the threads in a given width of cloth, to determine the fineness of its weave and so the quality.
Français : Compte-fils