Raymarine E90W User Reference Handbook page 122

Item Description
6 Ship's Heading Marker (SHM)
7
Ship's position
8 Motion Mode
9 Radar scanner status
10 Waypoint
11 Range ring spacing
Typically, your vessel's position is at the center of the display, and
its dead ahead bearing is indicated by a vertical heading line, known
as the Ship's Heading Marker (SHM).
On-screen targets may be large, small, bright or faint, depending on
the size of the object, its orientation and surface. If using a non-HD
digital radome scanner, strongest target returns are displayed in
yellow with weaker returns in 2 shades of blue. If using an HD or
SuperHD digital radar scanner, stronger target returns show as
different colors from a range of 256 colors, providing better clarity.
Be aware that the size of a target on screen is dependent on many
factors and may not necessarily be proportional to its physical size.
Nearby objects may appear to be the same size as distant larger
objects.
With experience, the approximate size of different objects can be
determined by the relative size and brightness of the echoes.
You should bear in mind that the size of each on-screen target is
affected by:
• The physical size of the reflecting object.
• The material from which the object is made. Metallic surfaces
reflect signals better than non-metallic surfaces.
• Vertical objects such as cliffs reflect signals better than sloping
objects such as sandbanks.
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• High coastlines and mountainous coastal regions can be observed
at longer radar ranges. Therefore, the first sight of land may be a
mountain several miles inland from the coastline. Although the
coastline may be much nearer, it may not appear on the radar
until the vessel is closer to shore.
• Some targets, such as buoys and small boats, can be difficult
to discern, because they do not present a consistent reflecting
surface as they bob and toss about in the waves. Consequently
these echoes tend to fade and brighten, and at times disappear
momentarily.
• Buoys and small boats often resemble each other, but boats can
often be distinguished by their motion.
Note: A GPS receiver and a fast heading sensor are required
for MARPA operation, and to maximize radar/chart overlay
performance.
E-Series Widescreen User reference