How:This design is easy to use. Simply place the card on the surface of the magnetic material and it will display a patterned magnetic field. Great for personal or scientific research. It can help us study magnetic fields that we can't see. It can be used for quality control, product demonstration, reverse engineering, certification, and educational purposes. Small and portable, lightweight, easy to carry. A great educational tool that will pique our interest in learning. The magnetic field viewer is a micro-encapsulated film that allows the user to see the static magnetic field. Highly flexible film is suitable for magnetic surfaces with any protrusion or cavity. Specification: Dimensions: 50x50mm 25 25mm 30 30mm Color: Dark Green Quantity: 1 Piece Package Included: 1 x Magnetic Field Viewer Transition: 1cm=10mm=0.39 inch Due to manual measurement, please allow 1-2cm error. Make sure you don't mind bidding. Due to differences between different monitors, the picture may not reflect the actual color of the item. Thanks!