|How does a VCR Plus system work? Are codes built in for every possibility of channel and time or does it calculate somehow? I know that if you enter a random number (including single digits) that some program is scheduled. — LK, Huntington, West Virginia
The VCR Plus codes contain just enough information to tell the VCR what time and day a program starts, what channel that program is on, and how long it will last. What is remarkable about these codes is not that they exist, but that many of them are so short. A long number that contained the complete date, the entire channel number, and the length of the program in minutes would obvious fulfill the requirements, but the actually numbers are never that long. While I don't know the precise encoding scheme, the date is clearly compressed—a daily or weekly program is represented by a very small code—and so is the record time for programs with a common duration. The VCR Plus codes get significantly longer when they must represent one-time only shows and shows with complicated durations. Even then, the date is truncated so that there are no current codes to represent a show five years in the future.