NorthStar 951X Operator's Manual page 175

Chapter 11 - Customizing the Unit
high degree of accuracy. Shorter averaging times, however,
give you a quicker-changing display of your speed, but with
less accuracy.
You can change the speed averaging value at any time without
affecting other 951/952 navigation functions.
To change the speed averaging value, press the (',7 menu
key. Press the &85625 3$' to select an averaging time of
between 2 and 10 seconds—or OFF. Press the (17(5 key to
make the change, or &/($5 to leave the option unchanged.
As discussed earlier in "Comparing GPS and loran" on page 25,
Changing beacon
the use of differential corrections enhances the accuracy and
frequency and baud
performance of your unit. One source of differential correc-
rate
tions is Northstar's fully automatic differential receiver, which
is contained internally within the 951XD or 952XD, or you can
connect a DGPS receiver to the 951X or 952X externally (see
the Northstar 951/952 Installation Manual for further details
on interfacing to external sources of differential corrections).
Differential corrections are invaluable when navigating in nar-
row or congested areas (such as ports and waterways), or
whenever extreme accuracy is required for locating a precise
area (retrieving lobster pots, returning to a diving spot, and so
on).
The Northstar differential receiver takes corrections broadcast
by shore-based marine radio beacons situated along most of
the U.S. coastline. These corrections are used by your unit to
improve its position accuracy to four meters—or better—with
one to three meters accuracy commonly available. Northstar's
two-channel differential receiver requires no manual opera-
tion. It automatically tunes to the appropriate differential fre-
quency as you move from one differential coverage area to
another, or as weather conditions change. Available radio bea-
con signals are constantly evaluated for signal quality by the
receiver, and only the best station is selected. As you travel,
the Northstar differential receiver is prepared to switch to
another frequency automatically, as conditions require.
951/952 Operator's Manual Rev. B Page 165