The radius of the outer circle and the center offset will determine the curve that you will get.[br][br]The center offset is how far the point generating the curve is from the center of the outer circle. In a real Spirograph, the offset cannot be greater than the radius of the circle. However, try adjusting the center offset to be greater than the radius to get some interesting curves.[br][br]When the radius of the outer circle equals the radius of the inner circle (that is, 2), the epitrochoid is known as a limacon.[br][br]Adjust the size of the point to get a thinner or thicker curve.[br][br]You can also adjust the speed of the animation with the speed slider.[br][br]When you've changed a parameter, hit the clear trace button to erase the old curve.[br][br]Use the pen circle button to show or to hide the generating circle and pen arrow.[br]