The internal accuracy of the unit is even better +/- 0.001. (The real life accuracy if your wondering is the worst cse scenario taking into account temperature, vibration and other elements that affect an accelorometer). ....they are very acurate units for measuing things like 0-100 and 1/4 mile times. when it comes to horsepower it has a real life accuracy of 3HP. readings however, will be lower