When shooting a film, the actors mark a scene for the camera crew just so the crew can get these measurements. Marking a scene means the actor goes through the motions, simply saying the lines without emotion so the technical problems can be solved. On big budget pictures, the stars usually have their stand-ins do most of this work. (A stand-in is a person who marks the scene for the actor.) When it comes closer to the time to do the scene, the star also participates in this technical rehearsal and for good reason. Besides the camera operator, the sound technician and boom operator need a rehearsal so they can conduct a volume check and make sure their microphones can pick up the dialogue and are out of camera range.