Built in compass - Do you adjust your deliniation?

[Flycaster]

I have a Shearwater PerdixAI with built in compass.
Do any of you set the deliniation on your compass to match your geographical area?
I'm wondering just how important this is.
?

 

[gcarter]

If you are following corrected directions, very. If they are uncorrected, not at all.

If you are marking your route so you can follow the reciprocal back, not at all.

I have never bothered as it has not been relevant to my navigation needs.

(Petrel 2 with compass, + wrist mount magnetic compass)

 

[RainPilot]

I don't bother, all of my nav needs are met with magnetic headings. If I was using a chart that was in True north, I might but so far not needed. In fact, the variation here is 1 degree so thats more accurate than I can dive anyway.

BTW, Variation is the difference between True North and Magnetic North. This changes depending on where you are.
Deviation is the difference between Compass heading and Magnetic heading. This is a factor of the individual compass construction, magnetic environment around it and will vary depending on which way the compass is facing. This is dealt with by the calibration process mostly, there will still be a residual deviation but normally pretty small, especially in diving applications.

1:60 rule. If you are off by 1 degree, after 60 distance units you will be off by 1 distance unit. I can't think when I have ever needed to nav on a compass for more than 200 yards underwater with no other references, if my compass is off by 5 degrees (a lot) I will be off by 50 feet. I can live with that in my application.

 

[Kohanbash]

Most of the time I am navigation short distances, or setting my own heading, so I can ignore the declination.

I find when I navigate with a compass it is important to keep looking around, that way if you are slightly off in navigation you will see what you are trying to find. Often I see people who keep there eyes on the compass and swim right past what they are looking for.

 

[tursiops]

The best compass thing I ever learned was to sight ahead at some object on my course, and then just swim to that object; repeat again as needed. No need (often) to glue one's self to the compass. this trick also can compensate for quite a bit of side-current.

 

[tbone1004]

I do if I'm navigating based off of maps. If I'm shooting my own bearings then I don't bother

@tursiops that doesn't work so well when you want to stay underwater the whole time....

 

[tursiops]

@tursiops that doesn't work so well when you want to stay underwater the whole time....

You misunderstand. I'm talking about sighting ahead to, say, a coral head, and swimming to it. No surfacing involved.

 

[tbone1004]

You misunderstand. I'm talking about sighting ahead to, say, a coral head, and swimming to it. No surfacing involved.

ahh, yeah that works. Most of my UW nav is with analog compasses on nav boards, so if I'm using a map I have to manually adjust. I don't like using wrist compasses for real nav at all, great for dead heading like that to make sure you are going in the right general direction, just not my preference for nav when you need to trust the compass