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as many satellites as it can "see" above the horizon, eliminates the
weakest signals, then computes its location in relation to those satel-
lites. Once the unit figures its latitude and longitude, it plots that posi-
tion 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-
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 differ-
ences in Section 6, Basic GPS Operations, on page 95.
Another portion of the unit’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. These
GPS Data Files (file format *.usr) can be shared between, not only the
LMS-334c iGPS and LMS-339cDF iGPS, but other Lowrance GPS units
and even personal computers.
Your 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 (Se-
cure 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 2 GB. (Compare that to a floppy disk's 1.44 MB capacity!) Your
unit uses all that MMC space for two key GPS purposes. (The MMC is
also used to record sonar logs.)
First, you can backup your onboard GPS Data Files by copying them to
the MMC. Since the MMC is 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 unit’s memory. (NOTE: No matter where they come from, GPS Data
Files must be loaded from the MMC into memory before your unit can
use them.)
The other key GPS use for MMCs is storage of special high-detail, cus-
tom maps, which you can produce on your computer with our MapCre-