Any professional post-production process relies heavily on timecode. Video systems work by presenting a series of still images a certain number of times per second to produce the illusion of movement. In PAL video based systems this is 25 'frames per second' and is the standard for British systems. Timecode 'counts' these still images and allocates each with a sequential number. This number has 4 parts of 2 numbers, the first pair representing hours and this goes up to 23 before returning to zero, the second pair is for minutes (59), then seconds (59) and the frames (24). The first timecode number that can exist is 00:00:00:00, and the last is 23:59:59:24. Proffessional video systems rely on timecode to be able to quickly locate where a particular piece of media is, and it can do this because a timecode is permanently recorded with the original media. Consumer based systems often only count the frames from where it starts playing for the first time and from zero. It is also advisable to transfer any non-timecode based material to a timecode based one before starting a post-production process.