The distribution method of magnetization NS level is opposite to that of the outside, and the magnetic induction line is also opposite to that of the outside. In order to distinguish NS grades, the first "indigenous method" is to find a magnetic needle, use a clothes needle or other needles, and rub it on the magnet several times to become a magnetic needle. First, hang the needle with a soft cord to form a compass. The hanging compass stopped, and the S pole of the magnetic needle was the one pointing to the north. The second method: magnets repel each other in the same stage and attract each other in different stages.