User manual GARMIN GPS GUIDE FOR BEGINNERS

[. . . ] GPS GUIDE for beginners © 2000 GARMIN Corporation GARMIN International, Inc. 1200 East 151st Street, Olathe, Kansas 66062, U. S. A. 913/397. 8200 or 800/800. 1020 Fax 913/397. 8282 GARMIN (Europe) Ltd. Unit 5, The Quadrangle, Abbey Park Industrial Estate, Romsey, SO51 9AQ, U. K. [. . . ] Parallel-channel receivers are quick to lock onto satellites when first turned on and they are unequaled in their ability to receive the satellite signals even in difficult conditions such as dense foliage or urban settings with tall buildings. 8 Sources of Errors Civilian GPS receivers have potential position errors due to the result of the accumulated errors due primarily to some of the following sources: · Ionosphere and troposphere delays -- The satellite signal slows as it passes through the atmosphere. The system uses a built-in "model" that calculates an average, but not an exact, amount of delay. · Signal multi-path -- Occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors. · Receiver clock errors -- Since it is not practical to have an atomic clock in your GPS receiver, the built-in clock can have very slight timing errors. · Orbital errors -- Also known as "ephemeris errors", these are inaccuracies of the satellite's reported location. · Number of satellites visible -- The more satellites the receiver can "see", the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. The clearer the view, the better the reception. GPS units will not work indoors (typically), underwater, or underground. Multipath Error Blocked Signal 9 · Satellite geometry/shading -- This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping. · Intentional degradation of the satellite signal -- The U. S. military's intentional degradation of the signal is known as "Selective Availability" (SA) and is intended to prevent military adversaries from using the highly accurate GPS signals. SA accounts for the majority of the error in the range. SA was turned off May 2, 2000, and is currently not active. This means you can expect typical GPS accuracies in the range of 6-12 meters (about 20-40 feet). However, accuracy can be improved by combining the GPS receiver with a Differential GPS (or DGPS) receiver, which can operate from several possible sources to help reduce some of the sources of errors described above. The next section explains DGPS and how it works. DGPS-How Does it Work? Differential GPS works by placing a GPS receiver (called a reference station) at a known location. Since the reference station knows its exact location, it can determine the errors in the satellite signals. It does this by measuring the ranges to each satellite using the signals received and comparing these measured ranges to the actual ranges calculated from its known position. [. . . ] Mounts -- When you need your hands free, a mount for your GPS can be useful. Many units come with a mount, and several additional mounts are available for other products in our line. Software -- Whether your need is to save your favorite waypoints or plan a trip, GARMIN's MapSource software can fit the bill!MapSource software allows you to view color maps on a personal computer, with zoom and pan functions for easy map browsing. [. . . ]