Clapperboard A clapperboard — sometimes called a clapper , slate , sticks , time slate , marker or one of several other names — is an important part of the camera department ' s toolbox used during principal photography . It has several different functions . The information written on it helps to organise the use of the filmed material in post - production . It also synchronises sound and picture recording by providing an absolute visual and auditory reference point that marks the very beginning of a particular camera ' s attempt to capture a scene or scene - part . Physical description . Typically small , hand - held devices , clappers have two pieces of wood or plastic hinged together so that they can be brought together to make a sharp " clap " . This noise is used as an absolute auditory reference for the synchronisation of the soundtrack of the scene . On most occasions during the filming of the BBC Wales version of " Doctor Who " , the board has had the traditional colours of " absolute " white and black , arranged in diagonal slants across the clapping mechanism . These colours are used because they ' re visible in almost any lighting conditions . However , the production team occasionally use multi - coloured clappers . Information on a clapper . Typically , clappers in the BBC Wales era have included the series number and the director and director of photography of a scene . Rarely , the producer ' s name has also been present . Perhaps more crucially , the clapper will contain : The clapboard also gives an indication of the basic lighting conditions the scene is supposed to have . The 2AC can choose between " interior " and " exterior " , and " day " and " night " . This is the only part of the clapboard which doesn ' t actually indicate the conditions " as they are " , but actually the conditions " as they ' re supposed to be " in the final product . Thus , a shot filmed on an exterior location at noon could be marked with " EXT / NIGHT " , if the director of photography is shooting " day for night " . If the scene being shot is one shot by , or having later composition by , the visual effect s department , the clapper will be given a code corresponding to a schedule worked out by the post - production supervisor or her staff . In this way , the visual effects department can better keep track of what special effect shot goes with which principal photography shot . Generation and maintenance of clapper info . Although clapper info is used by a variety of post production departments , it ' s important to stress the work of three people who are foundational to the information the clappers contain . The information begins with the writer , whose scripts designate scene numbers . These scene numbers are usually not tampered with , even if certain scenes are cut from the script . Scene numbers that are cut are merely omitted from the later flow of information , without causing a subsequent renumbering of the remaining scenes . These scene numbers are then written on the clapper , generally underneath the roll number . On " Doctor Who " the person who physically writes on the clapper is the assistant camera . The assistant in charge of actually writing the information on the slate will usually be the second assistant camera — that is , the " 2AC " . The 2AC is sometimes also called — but never credited on " Doctor Who " as – the " clapper loader " . This title is perhaps more descriptive of the actual job . Not only does he or she " load the clapper " with information , but he or she physically loads the camera with film . Thus , he or she is the person most aware of the minutae of the " roll number " — probably the most vital piece of information on the entire clapper . Typically unheralded — and never , as of 2010 , included in an interview on " Doctor Who Confidential " — the 2AC ' s job is absolutely vital to almost every other department . He or she starts the flow of information to the post - production departments . His or her counterpart in post is the assistant editor , whose job it is to organise all incoming foootage for the editor . For reasons of efficiency , however , almost all members of the post will organise their planning around the assistant editor ' s organisational scheme , which in turn is based on the scene number the writer provided in pre - production and the clapper loader gave in production . Use of clapper info by production staff . Almost everyone in every stage of production uses at least a part of the clapper information to accomplish their tasks in the preparation of the episode . However , there are perhaps three people who use the information most intently , aside from the editor himself . The sound design team use the physical " clap " of the slate to synchronise the sound recording . Using the clap as an absolute point of reference , they can perfectly align the visuals with the audio . Having an auditory anchor is essential to begin the process of layering in additional sounds . This anchor also makes it possible for the editor to later trim and reposition the scenes without fear that the sound might suddenly be out of synch . The visual effect s department needs the clapper info because their own work requires a separate numbering system . A single frame of film might require several different shots , as the visual effect required might take several different " layers " of filmed effects or CGI to accomplish . Thus , they need an internal system of numbering that they can then have the 2AC refer to with a single number on the clapper . The editor can later then request the shots from visual effects by referring to that number . Finally , the colourist needs the visual clues from the clapper to establish a baseline . Knowing what absolute black and absolute white look like under the lighting conditions of the shot is key to being able to subsequently grade the entire episode to a single colour standard . Use of clapper info by fans . Fans who take pictures of public location filming often snap photographs of clappers . They are the first clue fans get as to what an episode might contain . Because slates contain episode and scene information , fans can sometimes successfully piece together information about a scene just by looking at the episode and scene information on a clapper . If it ' s the " right " scene , they might even be able to guess at series - ending details . Clandestinely - photographed clappers can also be the first confirmation that fans are able to have that a particular director has been hired . During the run - up to Matt Smith ' s first series , photographs of clappers fueled the fire over how the series was going to be officially numbered . As can be seen in the photograph at top left , the clappers during production of this series clearly say " series 1 " . Since the series was actually the fifth produced by BBC Wales , photographs of clappers helped confirm the " series numbering controversy " to which Steven Moffat eventually referred in " Doctor Who Magazine " issue 417 .