There was too much information in my hand. I was walking north on Michigan Avenue, holding a Garmin, the super-advanced running watch that wraps around the wrist like a Wonder Woman bracelet. I had walked .15 — now it was .16 — miles. My pace was 15 minutes and 32 seconds a mile, but when I hurried to beat a light, it was suddenly 12:23.
The Garmin can tell me all this because it uses the Global Positioning System, or GPS, a network of 24 satellites, 12,000 miles above Earth, orbiting the planet at 7,000 miles an hour. The satellites were launched by the Defense Department, starting in the 1970s, to track enemy missiles headed for the United States. Because the satellites were meant for national security, the government built in a 150-foot error to discourage non-military users.
“They didn’t want direct hits on the White House,” said Robert Crawford, a salesman at the Garmin store on the Magnificent Mile.
That was close enough for boaters and pilots but not drivers, runners and cyclists. When President Bill Clinton abolished the policy, as part of the post-Cold War peace dividend, the technology became useful for auto navigation systems and for athletes who wanted to measure, to the hundredth of a mile, how far they had run or biked.
The satellites are arranged so a GPS receiver anywhere on Earth can receive signals from at least four at a time. The satellites combine their overlapping signals to pinpoint a user’s location, a process known as triangulation. Think of the signal areas as a series of spheres. Three spheres will overlap at two points, giving you latitude and longitude. Add a fourth, and voila, you’ve got altitude.
So even if you’re lost, as long as you have a GPS device on your wrist, you’ll always know exactly where you are. And how long it took you to get there.
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