This is a top-mounted downward slide-rule dial pointer (also referred to as a top-rail indicator or top-sliding glass dial pointer). It mounts along a top dial cord, guide bar, or track and extends downward across the face of a glass slide-rule dial scale. This style was widely used in 1930s and 1940s tabletop and console radio receivers from manufacturers such as Philco, Zenith, RCA Victor, General Electric, and Crosley.