That's a big misconception coming from a video on youtube done by guys who apparently have no idea how to use the g-tech. I've tested my gtech on a drapstrip in a couple of cars and the most it's been off is by 0.1 most times where in 0.01 - 0.02 ....

Also other videos ...
http://www.youtube.com/watch?v=2Tyozgkc7dE&feature=related

http://www.youtube.com/watch?v=mmfwg5eoAFs

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190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)