The script supervisor is a department head and plays a crucial role in the shooting of a film.
In that sense, they back up every department, monitor the script during shooting, and make sure that errors in continuity do not occur that would prevent the film from being able to be compiled smoothly in the editing room.
In pre-production, the script supervisor creates a number of reports based on the script, including a one-line continuity synopsis providing basic information on each scene such as the time of day, day in story order, and a one-line synopsis of the scene.
However, over the years, script supervisor positions throughout the American motion picture industry became more thoroughly integrated and formed a better balance among men and women.
The Academy of Motion Picture Arts and Sciences credits Sarah Y. Mason as the first script supervisor, having invented the craft of film continuity for director Albert Parker and the film Arizona in 1918, for which she was credited as "Continuity Girl.