It is a device used by a potter working at a wheel to make multiple copies of a particular item, like a mug. By setting the pointer at the desired diameter and height, the potter can more easily make duplicates.

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XXL - Science

It is a device used by a potter working at a wheel to make multiple copies of a particular item, like a mug. By setting the pointer at the desired diameter and height, the potter can more easily make duplicates.

XXL