GPS, the Global Positioning System, is now half a century old. This extraordinary technological advance routinely guides planes, ships, trains, automobiles, bikers and pedestrians with high precision. A Defense Department technology, GPS became widely available to the public in 1990. It has displaced and replaced some older navigation systems and brought revolutionary change to location and timing tasks.

To review some of the benefits GPS has brought, we talk with Michael Gallaher, of RTI International, who is co-author of a study of the benefits of GPS for the National Institute of Standards and Technology.