When Mel Fisher was looking for the Atocha, and really even after that, his main problem was how to search without leaving any gaps, or conversely, not overlapping searches. Also, he needed to do this in real time so that he could search efficiently, and record the results.
He tried a variety of methods, like any smart THer, and they changed as technology changed. Believe it or not, just a few years ago, there wasn't any off-the-shelf computer program that did that. Now as he searches, he knows where he is and where he was days before and can navigate accurately.
I actually had a job offer from him to do just that sometime in the late 80's, but couldn't move to Key West because of a new daughter. It would have been a fun job working for a great organization. - Stay single
One of my fun demos for customers is to have them go out in a field with my GPS and bury a quarter a few inches under ground and press the 'magic' button. I will then navigate to the quarter, and without even looking down, I will dig up the quarter - it's that accurate.