Plotting Compass, 16mm-EIS-PH0820A offers a thoughtfully designed, durable resource for hands-on learning. Glass face Aluminum case Diameter: 0.6ÂÂ in. (1.3cm) Pack of 10 EISCO Basic Plotting Compass, 16mm (10) Plotting compasses Basic 16mm plotting compass with principal points marked. Glass face in aluminum case. These compasses provide a simple, teachable way to demonstrate magnetic fields in class. Simple use and easy readability make it straight-forward for students to map magnetic fields.