When I get back to PMEL I will be continuing work on a new extensometer designed to last 5 years on the sea floor . Besides having more batteries than the current version, it will have an acoustic modem so a ship can stop by every year and retrieve the data without having to recover the instrument from the bottom. The teacher made a mistake. It was either a case of brain lock or I was on auto-pilot several days ago when I reported that transponders signal each other with radio signals. The reason that submarines have to come to the surface to use radio communication is that radio signals don't transmit through water.
Transponders actually communicate with each other using acoustic, or sound signals.
Now that I have admitted to the only mistake I have ever made in my life, I am ready to explain how transponders are going to be important in the work that we are doing today. You may remember that three days ago, just before the storm, we had picked up the five extensometers from the sea floor and deposited them in the elevator. The elevator and the extensometers have been parked on the sea floor ever since, held in place by a wheel from a railroad car. Yes, you read it right, Old railroad car wheels are one of the most popular items used to anchor equipment to the sea floor. Not only are they plenty heavy, but when they are left behind the simply rust away.