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Chapter 13 - Customizing Setup Functions
Distance,
bearing, and
steering
calculations
Page 13-22
1. At the NAVIGATION SETUP screen, press the CURSOR
PAD to highlight the MAG VARIATION option, then press
the EDIT key.
2. Press the CURSOR PAD left or right or press the LEFT
ARROW or RIGHT ARROW keys to select TRUE, AUTO, or
MAN (for manual).
3. When done, press the ACCEPT key (or CANCEL to leave
the option unchanged).
If you've chosen MAN, press the EDIT DATA key, then use
the KEYPAD to enter the variation for your area. If you
make a mistake during data entry, press the LEFT
ARROW and RIGHT ARROW keys to position the cursor.
To change between east and west variation (west is appro-
priate on the East coast of the U.S.), press the ARROW
keys to position the cursor, then use the KEYPAD to
choose either E or W.
4. When done, press the ACCEPT key (or CANCEL to leave
the option unchanged).
5. Press RETURN to go back to the SETUP MENU screen.
The shortest distance between any two points on the surface
of a sphere, appearing as a curved line on a Mercator grid, is
known as a great circle. By comparison, a constant direction to
your destination is known as a rhumb line, which appears as a
straight line on a Mercator grid. Over long distances, a rhumb
line provides a somewhat longer route of travel than a great
circle route; however, if a great circle route takes you too close
to bad weather or an unavoidable land mass, you may want to
follow a rhumb line. The 961 uses a rhumb line as the default
method for calculating distance, bearing, and steering (XTE) to
waypoints.
You can tell the 961 to calculate distance, bearing, and steer-
ing to your destination along either a great circle route or a
rhumb line:
If your starting and ending points are under 100 nm apart, great cir-
cle and rhumb line paths are practically the same.
NOTE:
961 Operations and Reference Manual Rev. D
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