A fish that sits at the edge of the antenna field can cause thousands of records to be created. The datalogger creates a detection record when the tag has left the field but since the tag is at the edge of the field the tag is seen/not/seen/not repeatedly all day.
The Max Gap parameter on the Setup screen of the PDA (and the MG command) are used to combine all of these "stuttering" detections into one. By setting a maximum gap of 5, if the tag is not seen for a few scans but reappears on the same antenna then the small gap is ignored. When the tag is gone for the number of scans in the parameter the detection record for the entire event will be written, ignoring the small detection gaps.
The factory setting for this parameter is zero so all detections are accurately recorded including the small gaps.