Raymarine Raydata Installation And Operating Handbook page 54

Chapter 6: The Display Pages 45
This display shows the depth in metres, feet or fathoms, depending on
the choice made in the Setup pages (see Chapter 4). The letter in the
lower right corner indicates the depth offset: that is, whether the depth is
measured from the keel (K), waterline (W) or transducer (T). The depth
offset is determined by the Setup selection, together with the response.
Note: If the depth data is being repeated from NMEA, the alarms and
depth offset specified for the RayData have no effect, and no depth
offset letter is displayed.
The trend arrow at the right edge of the display indicates the direction
and rate of change of the depth. An upwards arrow means that the
bottom is rising: that is, the depth is decreasing.
The length of the trend arrow indicates the speed with which the value is
changing. The arrow consists of up to six segments, including the arrow
head. The more segments are displayed, the greater the difference
between the current value and that shown in the previous update of the
display.
An alarm indicator (shallow or deep) is displayed at the bottom of any
screen if the depth value is outside the specified safe range, as
described in Chapter 5.
If the depth echo is lost, the display shows dashed lines for the missing
depth value, together with the last depth reading received, as shown in
the following example.