are the last pensions? we're running on borrowed time here. >> i think the pings can last up to 45 days. so i think we have some time here. the diminishing sound effect that angus houston referred to during his press conference can be related to a number of things. the diminishing battery life, topography of the ocean floor, the consistency of the ocean floor, relative to the silt, what's the depth of the silt and consistency of the silt, and the just basically shape of the bottom. it can change the way the pings are heard and the magnification. in addition to that, there are various temperature layers, as you move down in the ocean and that changes layers' ocean density, that can also play havoc with locating these pings. >> david, next step, theoretical