Let's study the way films were made 40 years ago :

Films like Ben Hur, Gone witht the Wind, 2001 : a Space Odyssee...and thousands of others, have been shot with a traditional clapper-board and edited on a film editor. Don't be afraid, I shall now explain...

First, let's describe a shooting in those days :

The picture is "recorded" by the camera on photographic film (seldom other than 35 mm). The camera's motor is driven by a quartz circuit (which guarantees an extremely regular motion of the film, with a theoretical drift of +/- 1 frame/day), and runs at 24 frames/second.

Separately, sound is recorded on a Nagra or Stellavox type tape recorder, on 1/4" tape, in mono (NAGRA III or IV, for ex.) or stereo (NAGRA IV-S). The tape recorder's motor is also quartz driven, and runs at 15 ips.

Since these two elements (picture and sound) are recorded separately, a vocal announcement followed by a clapper-board is performed at the beginning of each shot : this is called a "slate". The object of this slate is to systematically establish a sync point at the beginning of each take (or at the end of the take, if it isn't possible at the beginning. In that case, the clapper-board is held upside-down, so it can't be mistaken for the next shot's slate, when processing at the lab). We mean by "sync point" any related event, present on several media, which can be used to synchronize them.
			here, the slate would be "Piranha three, fifteen-b, take three" ended, of course, by the shutting of the clapper.

Why go through all this with the clapper-board, will you say, since any event common to the picture and sound could be used instead : a glass hitting the floor, for example, or a door closing. It is true, but a lot more tedious when syncing sound.

It also happens sometimes that the closing of the clapper-board isn't on film. Maybe it has been closed outside the camera's frame, or an end slate had been agreed upon, then... forgotten at the end of the shot !!! It's a job like any other !

In this case, the sound editor will indeed have to hunt for a sync point elsewhere in the shot, praying that there is one ! The actors might not be doing anything "percussive" in that shot. The clapper-board is used to guarantee a sync point for each take, speeding up the syncing process when editing.

Let's admit that nothing went wrong during the shooting.

What happens then ?

Let's follow the different stages of the sound and picture processes :

Picture process	.	Sound process
The negative is developped. The takes that the director decided to print are printed in positive, and will be shown as dailies during the shooting. The negative is then set aside, it will be manipulated again once the editing is done. The printed takes chosen for dailies are given to the editor. It's a work copy. The takes are compiled in the correct order, on a reel, with several feet of leader tape at the beginning and end of each reel.       leader tape : opaque plastic tape, identical in format to that of the film : 16, 35 or 70mm. Also availible for sound, with static-free properties		The takes chosen by the director (sync sound), as well as the spot effects, due only to the production recordist's very own initiative, are transfered (technical term for "copied") on sprocketed magnetic tape, of identical format to that of the picture : 16 mm if the picture is in 16mm, 35 mm if the picture's in 35mm.           Sprocketed magnetic tape formats           16/35mm sprocket tape recorder : Magna-Tech Electronic 600-c To give you an idea of its size : it stands 7 feet tall.
As long as the sync sound of the shooting hasn't been synchronized to these pictures, the editor can no longer work.
To gain time (it is usually the assistant editor's job, or the sound editor's), the editor can mark each clapper-board closure with an X drawn in white crayon, on the exact frame where the two pieces of wood of the clapper-board make contact.		The clapper-boards are spotted one by one, by first listening to the vocal annoucement and jotting that down in white crayon (on the backside of the tape !), on the left side of the clapper-board. The closure of the clapper-board is then precisely spotted by scrubbing the tape (back and forth movement of the tape against the playback head), and marked with an X in white crayon.
.		It's now the sound editor's turn to have to wait for the editor to perform at least a basic cut of a scene to go on with his work
		To gain time, the sound editor can nevertheless prepare several elements : listen to the spot effects he wishes to use, the wild takes, etc... He'll isolate the set silences on separate reels, so they can be looped at the mixing stage.