Not sure what you are talking about mate, but I have noticed with some amusement that in the web cam pics she is always looking pissed off at her instruments!
The sensor can only read to a depth that is much shallower than the actual depth of water below her. Most heads have a maximum rated depth which when reached just gives "0.0" as its reading!
hers is probably just reading the transducer offset. mine (raytheon ST60) keeps showing the last reading, flashing. every so often it gets a stray reflection off bubbles, fish etc and the reading changes. it got a false reading of less than the alarm setting once when the chart showed 3500 metres of water. didn't half make us jump!