Factory tires, pressure, standard pressure are used, and if you change those things (like different tires), then it appears to be your responsibility, not the car maker.
The basic distance-measuring mechanisms (revolutions of an axle, tires, driveshaft, etc.) are generally used to create an "accurate" (as close as possible) odometer. No problem, although tire pressure and temperature, car loading, and even speed will distort the "distance" per revolution just a little.
From that, the analog (magnet and spring) speedometer could be adjusted to read almost anything, and was not very accurate over a wide range of speeds.
Modern electronic displays could show the corresponding "accurate" (calculated) speed that the CAN buss data often reveals, but the DISPLAYED value is generally different, showing a value higher than the -0% European boundry and lower than the US (around) +2% boundry. Or so it seems, roughly. I think. Perhaps.
