While a compass is a wonderful tool for navigation, it can also be used to help you find a specific location and return to it. Let’s say, for instance, that while diving you find an interesting spot that you would like to revisit on an upcoming dive without having to retrace your route back. You can use your compass to obtain reference points on the surface so you can return to that same location next time.
It is recommended that every diver carries a Surface Marker Buoy (SMB) when diving. That way, if you need to contact surface personnel, mark your location, or if you need an ascent line, you can send the SMB to the surface and ascend along the line. This is an ideal situation for the use of your SMB. Deploy your SMB and ascend to the surface.
Once you are on the surface, directly above the location that you want to mark, you will need to take two compass headings, preferably separated by at least 90 degrees, and each directed towards a fixed object. For example, a mountaintop, a landmark, a lighthouse or piers are all good options that are easy to locate again when you return to the site.
Align your compass in the direction of the first object and note the heading on your slate. Do the same for the second object.
Once you’re back in the general area of the location, pinpointing the site is fairly simple.
Enter the water near the dive site to be by arranging yourself in as close to the same orientation as possible, with the two objects from which you took your original headings.
Adjust your position until you achieve both of the original heading lines from the same position.
As you can see in the figure, the two lines will cross when you are in the same location from which you took the original headings.