$9.00Hypotrochoids are mathematical curves traced by a point in a circle (your pen) rolling around the inside of a bigger circle. These curves have been studied by mathematicians for centuries. Hypotrochoid formulas are complicated, but creating hypotrochoid art is easy and fun! AGES 6+ / CONTENTS: Hypotrochoid templates, gear wheels & gear rings, 3 pens (red, green, blue), 3D spectacles / 3.2oz. 3.5"x8"