GPS Used As Odometer
Recently, exercise enthusiasts have observed that an advanced Global Positioning System receiver (GPSr) with an odometer mode serves as a very accurate pedometer for outdoor activities. While not truly counting steps (no pendulum is involved) an advanced GPS odometer can accurately reveal the distance traveled to within 1/100 of a mile (depending on the model, perhaps 1/1000 of a mile). 1/1000 of a mile is approximately the distance of a single pace or 2 steps (1.609 m). Precise metric odometers have a precision of 1/100 or 1/1000 km, 10 or 1 metre(s) respectively.
A GPS with odometer mode is also an excellent and inexpensive means to verify proper operation of both the speedometer and odometer mounted in a vehicle.
Read more about this topic: Odometer