arc as to where this plane might be. it is every hour sending a ping or electronic handshakedown to see where this plane is. if it's closer, it's going to be in one of the tighter rings. by doing this, they were able to establish this idea that the plane moved through the rings in this fashion. why do they think it didn't go to the north? well, there's a lot of radar up there in different cities and towns and they probably would have seen it up there. but also, the shape of the earth is not exactly round. you great slightly different mathematical equation if you go that way as compared to the south. but just to make sure, they checked this equation they came up with against existing planes, planes that they knew were out there and they specifically knew the location of. it's sort of like if you did a test problem in arithmetic and