Humminbird 561 - Manual (Page 15)

the area under your boat, including the following items:
to the 500 Series™ Fishfinder.
Structure - Where fish may be hiding.
Thermoclines - Layers of water with different
temperatures that appear at different depths
and different times of the year. A thermocline
typically appears as a continuous band of gray
levels moving across the display at the same
depth.
Bait Ball
Fish - The Fishfinder displays fish as arches
and/or fish icons, and can be set to alarm
when a fish of a certain size is detected.
When a target is detected, a Fish ID+™
symbol appears on the display with the
depth displayed above it. The size of the
symbol indicates the intensity of the sonar
return. The unit will clearly show schools of
Bait Fish as "clouds" of different shapes and
sizes, depending on the number of fish and
boat speed.
Battery Voltage - The voltage of the boat’s
battery; can be set to alarm if the voltage falls
below a certain point.
Hollow Fish Symbol (see Fish ID+™)
Shaded Fish Symbol (see Fish ID+™)
RTS (Real Time Sonar) Window™
What’s on the Sonar Display 8