requirement is plus or minus one kilohertz. so it can be 37.5, 36.5 to 38.5. chris is right. there are a lot of reasons that you can begin to see a shift in the pinging, the pinging frequency and that's the kind of parameters he's talked about. so this is nothing to be disturbed by, it's just one of the pieces of evidence when you're in the real world and real world equipment it doesn't function quite the way the ideal system does. >> chris, turning to the chinese ship for one second one reason some were optimistic about this the chinese ship detected pulses at that 37.5 kilohertz frequency. that frequency is not chosen by accident. can you explain why 37.5? >> well, it's an ultrasonic frequency that's not readily found in nature. the reason for it is you want it to stand out in the band width.