NorthStar 972 Quickstart Manual And Reference Manual page 153

ence between the angles to the two poles is
known as magnetic variation.
You can display bearings as true (relative
to north) or magnetic (to match your
compass). The 972 calculates the magnetic
variation for your position automatically.
Push the cursor pad up or down to choose:
The factory default setting is "automatic." Under
most conditions, you'll want the 972 to calculate
the variation automatically for your position,
since the automatically calculated variation is
usually entirely adequate.
Choosing the speed averaging time
When you're using uncorrected GPS, you
may see that your Speed-Over-Ground
readings are slightly erratic, varying by up
to several knots. The 972's GPS speed aver-
aging function can help steady these
readings by lengthening the time over
which your speed is averaged, from two to
ten seconds. Averaging can also be turned
off for the quickest possible reaction time.
Reference Manual Revision B
true — no variation applied (true
•
bearings are usually required when
using a gyrocompass)
magnetic — the unit calculates variation
•
automatically according to your
location and the date
Shorter averaging times provide a faster
display of speed changes, but with less
accuracy. A longer averaging time is useful
at lower speeds when you require the
steadiest readings and highest accuracy,
such as when you want to trawl at a certain
optimum speed.
Adjusting satellite elevation
The lowest sat elevation option is used
mainly for technical applications, in which
the 972 must track all visible satellites
regardless of how low they are on the
horizon. In other instances where
high-precision fixes are necessary, you can
increase this setting to "hide" any low satel-
lites, thereby preventing their use as
sources of GPS position information, and
avoiding potential errors.
This option is adjustable from 0° to 25°, in
5° increments, but Northstar recommends
leaving this option at the factory setting of
5°.
Choosing a geodetic datum
A variety of lat/lon coordinate models is
used by cartographers to produce the
world's navigation charts. Each model is
called a datum. The 972's geodetic datum
option contains all referenced datums,
Reference section 11 — Setup
Navigation options
149