Humminbird TCR ID-1 - Manual (Page 24)

USING THE TCR ID-1
OPERATING THE TCR ID-1
7. Depth Range
Automatic setting: on
The TCR automatically finds the bottom and then sets and displays the ideal depth
range when you turn the unit on. If you choose to leave the auto range change on, the
bottom will remain "blacked in" for easy-to-understand readings, and the depth ranges
will change automatically.
Or, you can turn the auto change off, allowing you to change the depth range manually.
In this mode, the bottom is not blacked in. This lets you see a double bottom echo,
which is preferred by some fishermen because the width of the second echo can
indicate bottom texture (see “Reading The TCR ID -I Screen” for details on using the
double echo).