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6
also called sonar charts or sonar graphs.) You can replay this sonar log
in the unit using the Sonar Simulator function, or play it back on a per-
sonal computer using our free Sonar Viewer. The viewer is available for
download from the Lowrance web site, www.lowrance.com.
You can save several different sonar log files, erase 'em and record new
ones, over and over again. The size of your sonar recordings is only lim-
ited by the free space available on your MMC.
How Lowrance GPS Works
You'll navigate faster and easier if you understand how your unit scans
the sky to tell you where you are on the earth — and, where you're go-
ing. First, think of your unit as a small but powerful computer. (But
don't worry — we made the unit easy to use, so you don't need to be a
computer expert to find your way!) It includes a keypad and a screen
with menus so you can tell it what to do. The screen also lets the unit
show your location on a moving map, as well as point the way to your
destination.
This gimbal-mounted unit uses an external antenna/receiver module,
which makes the whole system work something like your car radio. But
instead of your favorite dance tunes, this receiver tunes in to a couple
of dozen GPS satellites circling the earth. (It will also listen in to the
WAAS satellites in orbit, but more about that in the upcoming segment
introducing you to GPS and WAAS.)
Your unit listens to signals from as many satellites as it can "see"
above the horizon, eliminates the weakest signals, then computes its
location in relation to those satellites. 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-
making software, MapCreate™. Some unit features — such as search-
ing for businesses and addresses — won't work without a custom Map-
Create 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
6, Basic GPS Operations, on page 105.
Another portion of the unit’s onboard memory is devoted to recording
GPS navigation information, which includes waypoints, event marker