firstly, the effect of batteries. if the batteries keep dying, they can transmit intermitte intermittently. secondly, it may be the way the black boxes lying on the sea floor. they might be slightly buried. they might be obscured, and under particular condition, they're able to get their signal out. there could be two reasons that we are only seeing it inpatient mittently under -- intermitte intermittently under certain conditions in the ocean to find and listen and record. >> speak to this issue for me of finding, locating these black boxes and retrieving those. those two issues in and of themselves are an enormous undertaking. >> very much so. so, we -- to be absolutely certain that they have found the black box, they would actually have to eyeball it. and the eyeballing, taking a photograph, knowing exactly how