Scene Sync was a specialised form of motion control used to make the Doctor Who serial, Meglos. It somewhat solved a problem common to CSO work by slaving the camera trained on the model shot to the camera used to film the actors against a blue screen. This meant that the actors stayed in the same position relative to the background, adding to the overall believability of the composited shot.
In the CSO shots typical of Doctor Who up to this point, two different camera operators were required to accomplish a final shot. One had a camera pointed at a background, while the other had a camera trained on actors. It was laborious in the extreme to ensure that the two cameras were working in harmony. Even the slightest lens movement could make the actors appear to "slide" across the background, or even disappear behind a portion of the model shot. The difficulties of using CSO can plainly be seen in a serial like Underworld, or even in part four of Robot.
Scene Sync attempted to solve these problems by eliminating the second camera operator. However, it introduced a new problem. Because the model's camera was invariably smaller — and indeed focused on a smaller area — the camera operator could easily make movements that would make the smaller camera lose its subject. If a model was at 1/10th scale, for instance, then the camera on the model could only move 1 centimetre for ever every decimetre that the actors' camera moved. Scene Sync technology, however, was never developed far enough that the operator could just type in a scale for the lower camera. Instead, the operator had to manually fiddle with a dial until the two cameras more or less moved together properly.
Still, Meglos proved the technology could work to an acceptable standard, and the BBC used it in a few other, non-Doctor Who projects. Scene Sync was never used again on Doctor Who, and it quietly faded away from all use on the BBC. By the mid-1980s, CSO itself was being phased out as a technology used by drama series, meaning that there wasn't really a need for this kind of motion control technology. (DOC: The Scene Sync Story)