OBDII scann tool

[Justin McClanahan]

How does it accurately give you acceleration numbers without having some
sort of g-force meter in the unit?  How does it know if you're just
spinning tires or actually moving forward?  I'm guessing it goes off of
gear ratios and tire size, but how does it know how fast you're actually
accelerating?  Theoretically I could just row through the gears up to
100mph (say like in the rain) never move an inch, but because my front
tires were moving it would think that I have just run the 1/4 mile,
right?

Just curious....

Justin McClanahan
95 G20 w/ VVL