The same film is used by professionals such as engineers, developers and researchers to find out the magnetic field distribution when a group of magnets is involved. It is also used in the manufacturing industry to form the internal defect of a steel part in conjunction with an X-ray machine. The green foil contains millions of nano magnetic particles that can rotate freely when you are near a steel object or a permanent magnet. When the magnetic particles change their orientation, the reflection rate of the light also changes to the magnetic field below. This is why the film changes shades when a magnetic field is applied. The film becomes darker when the magnetic field lines are perpendicular to the surface, and brighter when the field lines are horizontal, i.e. across the surface. When a rod is placed under it, the magnet will appear as a darker area with a lighter outline. When both poles are placed under the film, the areas near the two poles are dark, but the edge of the two poles is displayed as a light line, so you can determine the pole orientations. Our images show the two same dimensions, but differently magnetized. The film is also highly flexible and can be easily wrapped around magnetic assemblies. Tips & Uses: 1. Place the film near the magnet to observe the pattern changes so you can see how the magnet is magnetized and where the magnetic rods are located on the magnet. 2. The stronger the magnets, the better the results. We recommend neodymium magnets instead of ceramic magnets. 3. To achieve the same results of our pictures, you should use the same type and quantity of magnets. 4. The film identifies neither North nor South Poles. If you need a pole identifier, you can check out our pole detector offers. 5. Do not fold the film as it leaves a permanent crease.