The totally revised Geoliner blackboard compass will convince you by its superior quality and handling! With a super easy and safe mechanism you clamp the chalk into the compass. The vacuum cups are mad out of extra soft synthetics, that easily adapt to rough black board surfaces. That way the compass adheres perfectly.
It also has a cm- and degree- scale, that enables you to draw perfect arcs and radii. On one of the 2 blades there is a turning handle installed that additionally eases usage.