Simrad CE33 ChartSounder Manual page 152

Appendix A-6 CE33 Glossary of terms
tions for most of the losses and absorption that occurs as sound energy passes
through sea water. There are three settings to choose from, Normal, Special
and OFF.
The setting "Normal (20 log R) is for general fish finding at depths down to
50m (150') and it will also give a uniform bottom echo presentation at shallow,
mid and deep water.
The setting "Special (40 log R) will adjust the TVG to show the same echo
strength for a given size fish at varying depths.
The OFF position is used for net sounders. In OFF position the TVG is inac-
tive which means that the sounder operates with a fixed gain between each
transmitter pulse. Auto range is switched to manual.
White line – is a control which places a white/black line at the displayed sea
floor and blanks out 4 pixels just below the line. The purpose of this is to help
the user detect targets, such as fish, which are very close to the sea floor and
whose echoes tend to merge with those of the sea floor itself.
VRM – Variable Range Marker – this refers to a horizontal black line shown
on the display screen. The user can measure the range to targets shown on the
display screen by use of these VRMs. The depth to the VRM can be seen in
the left side of the screen. This function is not available if VRM expansion is
ON.