I scratch tested the camera and it passed with flying colors. The interior mechanism is known as a Unit I (Unit Eye) shuttle. This is one of the features that makes the 2709 the best camera of its day. Specialeffects were being done in camera in 1918, and this camera has a rotoscope Unit I that allows for viewing your scene, on the film, through the viewing tube in the door. This type of camera had a rackover system that took time and effort to operate. The Director of Photography had to get the camera into position so that he could view the scene through the lens. Rotoscoping the camera allowed for viewing and setting of critical focus without having to move the camera to another position. This, along with a rock steady image, made 2709's very popular cameras for screen titles and animation.