Underwater compass is used for navigation. Compass works with the Earth’s magnetic field.
It is reliable and being used for hundreds of years for navigation on the seas. A compass doesn’t get affected by the angle of sun, by pressure, visibility or water.
Here is how to use a compass for going straight underwater:
- Hold the compass exactly parallel to the surface/bottom
- Point the lubber red line to your direction
- Turn the bezel (turning ring on the compass) while holding the compass fixed. Needle pointing the North should be pointing the notch (pointing the 0 °).
- Always keep the needle pointing the notch while fin-kicking. You’ll be going exactly straight.
- When you want to return to shore/boat, turn 180°. You’ll do this by turning from the previous position till the needle points 180°.
- Turn the bezel again till the notch comes right in front of the needle (needle should point 0° again). Great job! You are heading to your starting point again.
Here is a video from expervillage you can watch what I have talked about above.
Underwater compass usage should be learned from a dive professional. There are such specialty courses in dive agencies. Generally named “underwater navigation“, these specialty course not only teaches you how to use a compass but also the natural navigation (read Continuous Training).
I advise you to buy a compass as an addition to you dive console. That’s because you are saving a room for one piece of equipment. You cannot forget/lost your compass.