NorthStar 958 Operator's Manual page 149

Chapter 10 - Understanding Radar Functions
As you change Point A or B, the numbers in the upper
right-hand corner of your screen change to show the new
location of the point.
You may want to generate an alarm when an echo of a certain
minimum strength occurs within the zone, indicating an
object within the guard zone. Press the TRIGGER LEVEL key
repeatedly to set the signal strength that causes an alarm: low,
medium, high, or off (no alarm). You can set the alarm to be
visual only (a white circle flashes to pinpoint the alarm) or
both visual and audible (see "Changing alarm settings" starting
on page 152).
The alarm is temporarily disabled while you adjust the trigger
level. It automatically restarts if a minute passes with no
further adjustments. When you press DONE, the alarm is
enabled.
Range rings are concentric circles around your vessel, that
Radar markers
appear on the screen at fixed intervals. These rings are
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controlled by the radar and represent distance. You should be
careful to note the spacing of the range rings. An object three
rings away would be 1.5 nm miles from your vessel if range
rings are 0.5 nm apart; however, it would be 15 nm from your
vessel if range rings are 5 nm apart. The spacing of the range
rings is shown in the upper left-hand corner of the radar
image.
Press the following keys to turn the range rings on or off, and
to change the bearings.
Press the RANGE RINGS key repeatedly to turn the range
rings on or off.
Press the Bearings key repeatedly to display radar bearing
digits as relative to the vessel heading, or as True bearings/
Magnetic bearings (see "Choosing magnetic variation" starting
on page 169).
958 Operator's Manual, Rev. A Page 141