sentence: It gets its name from its operating principle, the tangent law of magnetism, which states that the tangent of the angle a compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields.
modified: fix grammar: It gets its name from its operating principle, the tangent law of magnetism, which states that the tangent of the angle an compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields.