The PDA GPS of Your Dreams
What could be more convenient than a hand-held device that reminds you appointments, stores your records and tells you how to get there? Adding a GPS system to your personal digital assistant is one of the latest ways to upgrade your PDA.
How Precise do you need to be?
As usual for new technology, the price of a PDA GPS depends in part on the amount of help you want in the global positioning department. The GPS unit alone allows you to send a signal to the network of satellites surrounding the earth. The signal transmits the time that it was sent and the three or four satellites not blocked by the earth compare the time with the time the signal was received.
Each satellite calculates the amount of time it took for the signal to reach it and they all compare those time calculations and the position of each satellite with each other to come up with a triangulation of your position. It takes the information from three satellites to gather enough data to come up with your latitude and longitude. A fourth satellite can add enough extra information to figure your altitude, too.
Before you add a PDA GPS, you should ask yourself how precise you need your information to be. Although all PDA GPS units depend on information from the same satellites, the precision of the data is affected by the precision of the time-keeper in your PDA or GPS.
The satellites themselves are equipped with extremely precise atomic clocks. Your PDA GPS won't have a clock quite that precise or quite that expensive. If you don't think you'll need to know your position to within a foot or so, you can opt for a PDA GPS unit with the less expensive time piece.