GPS units are sometimes used to track high-value items, such as laptops and cars. Tracking with GPS produces highly accurate results, but atmospheric conditions can distort results.

GPS satellites run by the Coast Guard provide accuracy to at least 7.8 meters 95 per cent of the time, according to the Coast Guard's GPS website. Users in general will likely have better accuracy than this most of the time.

The real-world accuracy of GPS tracking depends in part on the quality of your unit. The best units have accuracy to within 3 meters 95 per cent of the time, according to GPS Basics.

As of 2010, the GPS system used by the military -- called Precise Positioning System -- is more accurate than civilian GPS units. In some areas of the country, Wide Area Augmentation System satellites increase accuracy to better than 3 meters, according to Garmin.