Furuno FA Manual page 255

DBT - Depth below transducer
$--DBT,x.x,f,x.x,M,x.x,F*hh<CR><LF>
| | | | | | |
| | | | | | +--------- 4
| | | | +--+----------- 3
| | +--+----------------- 2
+--+----------------------- 1
1. Water depth, feet
2. Water depth, m
3. Water depth, fathoms
4. Checksum
DPT - Depth
$--DPT,x.x,x.x,x.x*hh<CR><LF>
| | | |
| | | +----- 4
| | +--------- 3
| +------------ 2
+---------------- 1
1. Water depth relative to trancsducer, in meters
2. Offset from transeducer, in meters(see notes 1 and 2)
3. Maximum range scale in use
4. Checksum
NOTE1 "positive"=distance from transeduser to water-line.
"-"=distance from transducer to keel.
NOTE2 For IEC applications the offset should always be applied
so as to provide depth relative to the keel.
APPENDIX
AP-11