(covers information from several alternate timelines)
An astrogator was a device used for navigation, common on Constitution-class starships. (TOS: "The Gamesters of Triskelion") Located between the helm and navigation stations at the forward section of the bridge, the helmsman could change the ship's heading simply by turning the dial upon the face of the astrogator. (TOS: "And the Children Shall Lead")
See also Edit
Although Franz Joseph's Star Fleet Technical Manual described this navigational device as an "astrogator," it was never actually described as such in dialogue in any Star Trek episode or film.