https://www.zgallerie.com/p-10870-hypotrochoid-art-set.aspx?source=myregistry
Hypotrochoid is the mathematical term for a line traced by a fixed point in a circle rolling around a bigger circle. These beautiful flowing curves have fascinated mathematicians for centuries. Different points within the circle produce wildly differing patterns. A classic and absorbing drawing set, easy and fun to use. 11 piece set in a tin including 2 hypotrochoid templates, each with 3 gears, plus red, green and blue pens.