Knowing how to properly use a dive compass compensates for the lack of clear underwater markers and possible disorientation. If you ever get separated from your buddy, having an idea of where you were and where you were going can help you backtrack and find them.
The best scuba diving compasses might be more detailed but a simpler design with a focus on the cardinal directions can already make a lot of difference if you know how to read it. Some people even consider it one of the ways of how to prevent vertigo when scuba diving.
How to Use a Dive Compass Underwater
So, take the necessary safety precaution and learn how to read a dive compass. There are two ways to do it, one is more precise and one is a simplified version, but both are valid and should help you stay calm with good orientation underwater.
The Proper Way Using Degrees
This method goes by the numbers or the actual degrees shown on the compass. Note that in some designs the cardinal directions replace the degrees;
N = 360°
E = 90°
S = 180°
W = 270°
For this method, you might want to use the bezel because it has clearer markings of the degrees. Adjusting the bezel can also help you do the calculations.
- Stay as still as possible with neutral buoyancy or at the very least swim in a straight horizontal line. This gives you the most accurate reading.
- Hold the dive compass as horizontal as possible and check that you have an accurate reading by twisting the face along an imaginary horizontal axis.
- The reading is accurate when the card i.e. the indicator pointing north remains the same.
- Make sure the lubber line is pointed in the direction you wish to go. A lubber line shows the exact direction you are heading towards which makes reading your compass easier.
- Note the direction in degrees.
- Returning to your origin simply means 180° in the opposite direction. If the compass has a lubber line then you won’t have to do any calculations because you can simply read off the degrees on the other end of the line.
If there is no lubber line, you have to either add or subtract 180°. You know that you have the correct direction when the answer is between 0° – 360°.
- For a right turn, add 90° to your current direction. If the answer is greater than 360° then you have subtracted 360° from that number to get the correct direction.
- For a left turn, subtract 90°. If the answer is smaller than 0°, in other words, a negative number, then add 360° for the correct direction.
Going By the Markings for Fewer Calculations
Alternatively, you can do somewhat simpler calculations by determining the directions based on the markings and cardinal directions instead of the degrees. This method is less precise but some occasional recreational divers might feel more comfortable with it.
For this method, you have no need of the bezel so you don’t have to adjust it in any way.
- Stay as still as possible with neutral buoyancy or at the very least swim in a straight horizontal line. This gives you the most accurate reading.
- Hold the dive compass as horizontal as possible and check that you have an accurate reading by twisting the face along an imaginary horizontal axis. The reading is accurate when the card, i.e. the indicator pointing north, remains in the same position.
- Make sure the lubber line is pointed in the direction you wish to go.
- Note the direction as the number of markings before or after the nearest cardinal direction. For example, S + 2 markings.
(Most compasses have a marking for every 30° but this may differ per design. However, in this case, the actual value of the marking does not matter.)
- To return to where you started, you should head for the opposite of S + 2 markings which would be the opposite cardinal direction plus the same number of markings. In this case that is N + 2 markings.
- To make right turn, head east plus the number of markings from your original direction. A perfect right turn from S + 2 markings is heading towards E + 2 markings.
- To make a left turn, take the same idea but in the western direction. In this case that is W + 2 markings.
