Back in my college days, I owned a turntable that had a main arm and a smaller lighter auxiliary arm. The cartridge head could pivot slightly in the horizontal plane. This meant that as the arm swung from the outermost groove area toward the innermost, the angle of the cartridge remained very close to 90 degrees from the radius of the groove at all times. An example of this method can be seen on a windshield wiper that has two parallel arms for a single blade assembly. As the wiper arms move through their arc, the blade can remain vertically oriented, instead of changing its angle of attack as the angle of the main wiper arm changes.