Once a camera position or overall "shot" is established by the director of photography and camera operator, the 1st AC begins to measure the various distances between the actors' marks and the focal plane of the camera. These distances are recorded in a series of grease pencil/pen marks on the focus barrel of the lens, and/or the marking disc or ring on the follow focus device. Traditionally, the focus puller used only their marks and their own well-developed sense of distance estimation to achieve good results. Over the last decade, the increased use of digital cameras, higher-resolution video taps and/or on-camera monitors have provided focus pullers with additional tools to help maintain proper focus. A high-definition monitor can be particularly useful when a fast-paced production simply does not allow time for the focus puller to set and check all marks that may be needed, or if no rehearsal will be provided.