underwater pings were a lead that needed to be pursued. >> that was cnn's renee marsh reporting for us. we want to go to our expert, mike exner who joins us from boulder, colorado. he's a member of this outside group of experts. >> mike, thank you so much for being with us. i know that you say your 80% to 90% confident the plane is in this particular place in the southern indian ocean. but in laymen's terms, can you explain to us why you are so certain? >> well, first of all, i wouldn't say that we're certain. i think this is the highest probability location. it has to be somewhere along the arc. it's along this seventh arc. the question is, where along the arc. the primary assumption that