This size-adjustable circular ruler provides the ability to draw or measure circles and arcs by simply expanding and contracting it to the desired circumference. It snaps easily into place for a semi-permanent hold and displays both diameter and arc length measurements. It can be used to measure and inscribe onto 3D objects like spheres, cylinders and cones. Its flexible plastic construction is safe for all ages, as it has no needle or sharp points. Available in both U.S. standard or metric scales.