It allows altering shift points for changing conditions among other things. Example, in the recent Singapore F1 Grand Prix a driver was experiencing major electrical problems which caused his pit lane speed limiter to not work, so engineering told him to keep it below the red lights in first gear instead. Other times they may be told to shift in the yellow, etc.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.