GPS is an acronym for Global Positioning System. The System is a whole network of satellites that surround the earth and transmit information back at all times. A pocket GPS receiver is a handheld GPS navigator unit that can receive information from the satellites in order to pinpoint a certain location on the earth, using longitude and latitude.

The Three Parts Of The GPS

The Global Positioning System has three segments to it: the space segment, the control segment, and the user segment. The "space segment" are the satellites. These 24 satellites are orbiting the earth at about 12,000 miles above the earth. Being so high allows them to cover a great area.

The way the satellites are spaced out around the earth, a pocket GPS receiver can always get a signal from at least four of them at once. These satellites (that the pocket GPS receivers use) are traveling at 7,000 miles per hour – circling the earth every 12 hours. They use solar energy for power, but have backup batteries. They transmit back to the earth in "line of sight", so they go through clouds, plastic, and glass, but not through mountains or buildings.

The "control segment" consists of the five control stations on earth. They track the satellites and give them corrected time and orbit information. There is one "master control station" that the other four send information to. The master control station determines what the satellite needs to know, and it sends "uplinks" to the satellites that the pocket GPS receiver is getting information from.

The "user segment" is each individual person with their pocket GPS receiver. They can be a wide range of people, with a large range of hobbies or work. These include hikers, pilots, boaters, hunters, and the military. It also includes geocachers, those playing the "treasure hunting" sport elaborated more online at geocaching.com. Anyone who wants to know where they are, where they've been, and where they're going will benefit from having a pocket GPS receiver.

Is it 100% Accurate?

That would be nice, but it is unrealistic to expect that a pocket GPS receiver can be totally accurate, given all the things that can cause errors in the data. A few of these causes are: a delay in data from the layers in the atmosphere, tall buildngs or mountains that the signal can bump against, errors in the clock in the GPS, inaccuracies in the reported location of the satellite, and not having enough satellites "visible". Some things that can interfere with your pocket GPS receiver. The clearer the view of the sky, the better it will work.