VCR Plus+, G-Code, VideoPlus+ and ShowView are different names for essentially the same system that has been used to program previous generation of video recorders without on-screen displays.
Before the advent of on-screen displays, the only interface available for programming a home video recorder was a small LED or LCD panel and a small number of buttons. Correctly recording a specific program was therefore a somewhat complex operation for many people; scores of jokes have referred over the years to the need to "have a 12-year-old" or someone technically adept to successfully program a home video recorder or to avoid having a perpetual blinking "12:00" on the recorder's display. G-Code, VideoPlus+ and ShowView were introduced to remove this difficulty.
The central concept of the system is a unique number, a PlusCode, assigned to each program, and published in TV listings in newspapers and magazines. To record a program, the number is taken from the newspaper and typed into the video recorder, which will then record on the correct channel at the correct time. The number is generated by an algorithm from the date, time and channel of the programme, and so does not rely on anything being broadcast over the air. This means it will not compensate for a disrupted schedule due to live sporting events or news bulletins, but many video recorders with these systems also incorporate Programme Delivery Control (PDC) and will use that to alter times if possible.
This system has been licensed to TV and VCR manufacturers in about 40 countries, but is known under different names. It is known as VCR Plus+ in the USA and Canada, G-Code in Japan, China, New Zealand and Australia, VideoPlus+ in Ireland and the United Kingdom and ShowView in the rest of Europe and also in South Africa. The system is called VideoPlus+/ShowView in Europe because Philips has a trademark registration for "VCR", and as G-Code ('G' for Gemstar) in Japan because VCR is not a common abbreviation there ('VTR' is used instead). However, because TV programs' schedules are different, the coding has to be adjusted in each of the regions and recording equipment is not interchangeable.
The actual algorithms used to encode and decode the TV guide values from and to their time representations were published in 1992, but only for 6 digit codes or less. . The demonstration applet, presented here, is likely derived from this code and also works with 6 digits only.
One problem found during reverse engineering efforts is that the algorithm seemed to change for seven and eight digit codes.
Acknowledgements and notes
This article reuses material from Wikipedia page http://en.wikipedia.org/wiki/VCRPlus under the rights of CC-BY-SA license. It is too similar and requires further work to integrate more sources.