The first step in making an LP is cutting a master lacquer. This is done by using a metal stylus attached to a coil placed within a magnetic field. All mounted on a radial-tracking arm. An amplified music signal is connected to the coil and drives it to cut a spiral groove in the rotating lacquer disk. So using a mc cartridge is just the reverse of this process! "As it was in the beginning, so shall it be in the end".