The Deluxe Compass Set with Re-Magnetizing Storage Tray is the perfect way to store compasses. The set includes 20 compasses presented in a metal stackable storage tray that is equipped with two magnetized walls (top and bottom) facing each other to retain the alignment of the compass needles. The storage tray also features a calibration zone with embedded Neodymium magnets that can re-magnetize the compass when necessary and ensure that the red needle points N (North). This allows students to ensure consistent results across classroom experiments. Each compass has a 40mm diameter.