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Once the unit figures its latitude and longitude, it plots that position on the moving map shown on the screen. The whole process takes place several times a second! The performance doesn't stop there. Stored in the permanent memory of each unit is a basic background map of the entire world. We lock it in here at the factory — you can't change or erase this map. The background map is suitable for many navigation chores, but for maximum accuracy and much more detail, you need our optional map 6 making software, MapCreate. 6. Some unit features — such as searching for businesses and addresses — won't work without a custom MapCreate map. There is so much detail in our background map (and even more in MapCreate) that we'll describe their contents and differences in Section 3, Basic GPS Operations, on page 100. Another portion of the SeaCharter 500CDF’s onboard memory is devoted to recording GPS navigation information, which includes waypoints, event marker icons, trails and routes. This lets you look back the way you came. Think of this data storage like the hard drive memory in a computer or a tape in a cassette tape recorder. You can save several different GPS data files, erase 'em and record new ones, over and over again. Like any computer file, these GPS Data Files (file format *.usr) can be shared between Eagle GPS or sonar/GPS units or even personal computers. This unit has one more thing in common with a personal computer. Just as computers have a floppy disk drive for storing and exchanging files, the unit has a slot for an MMC (MultiMedia Card) or SD card (Secure Digital card) flash memory card. These solid-state memory devices are about the size of a postage stamp, but can hold data ranging from 8 MB to 1 GB in size. (Compare that to a floppy disk's 1.44 MB capacity!) This unit uses all that MMC space for two key GPS purposes. First, you can backup your onboard GPS Data Files by copying them to the MMC. Since the MMC is removable (like a floppy disk or a cassette tape), you can store these GPS Data Files on a personal computer equipped with an MMC card reader. (Or store them on a pocketful of MMCs, if you don't have a computer.) Our MapCreate mapping software can save, edit or create its own GPS Data Files, which can be copied to the MMC and then loaded from the MMC into the unit's memory. (NOTE: No matter where they come from, GPS Data Files must be loaded from the MMC into memory before the unit can use them.) The other key GPS use for MMCs is storage of special high-detail, custom maps, which you can produce on your computer with our MapCreate software. These MapCreate custom maps contain much greater detail than the basic background map. These Custom Map Files (file format *.lcm) can also be shared between Eagle GPS or sonar/GPS units and personal computers. This unit automatically reads Custom Map Files directly from the MMC or SD card. To use a custom map, all you need to do is slide an MMC containing a map into the unit. 7 8 Introduction to GPS and WAAS Well, now you know the basics of how the unit does its work. You might be ready to jump ahead to Section 2, Installation & Accessories, on page 15, so you can mount your unit and plug in the power. Or you might want to see how our text formatting makes the manual tutorials easy to skim. If that's the case, move on to "How to Use This Manual" on page 11. But, if you want to understand the current state of satellite navigation, look over this segment describing how GPS and its new companion WAAS work together to get you where you're going. The Global Positioning System (GPS) was launched July 17, 1995 by the United States Department of Defense. It was designed as a 24- hour-a-day, 365-days-a-year, all weather global navigation system for the armed forces of the U.S. and its allies. Civilian use was also available at first, but it was less accurate because the military scrambled the signal somewhat, using a process called Selective Availability (SA). GPS proved so useful for civilian navigation that the federal government discontinued SA on May 2, 2000, after the military developed other methods to deny GPS service to enemy forces. Reliable accuracy for civilian users jumped from 100 meters (330 feet) under SA to the present level of 10 to 20 meters (about 30 to 60 feet.) Twenty-four satellites orbit 10,900 nautical miles above the Earth, passing overhead twice daily. a series of ground stations (with precisely surveyed locations) controls the satellites and monitors their exact locations in the sky. Each satellite broadcasts a low-power signal that identifies the satellite and its position above the earth. Three of these satellites are spares, unused until needed. The rest virtually guarantee that at least four satellites are in view nearly anywhere on Earth at all times. A minimum of three satellites are required to determine a 2D fix. The system requires signal reception from three satellites in order to determine a position. This is called a 2D...