Perdix AI compass

[tbone1004]

I don't think that is quite right. I think that it only calibrates the magnetometer chip and, if equipped, also with accelerometer or gyroscopic chips. I believe declination to be a totally separate issue.

Declination is the delta between true north and magnetic north
Calibrating the compass tells the compass that magnetic north=true north so you don't have to manually adjust for declination for where you are diving

 

[stuartv]

I am lost.

It seems like I remember that to calibrate my Perdix compass I had to turn the Perdix around multiple times in all directions.

And, there is a separate setting where you set the declination. Am I not remembering that correctly?

And, I'm not really clear on how important any of those things are unless I'm trying to use the compass to follow a heading that somebody gives me from a calibrated compass or a map. If I'm just taking a heading using the Perdix and then using that heading (on my Perdix) during a dive, I don't see where the calibration and definitely not the declination setting matters. And that latter is all I have really used my compass for. Either, take a heading away from the shore, to be sure I can swim back to the shore without surfacing, or, take a heading from the anchor line along the wreck, so that if I get turned around, I can check my compass to have an idea of which way to swim along the wreck to find my way back to the anchor line.

 

[Charles2]

Declination is the delta between true north and magnetic north

Agree: Declination is both the magnitude and direction of the difference between true north and magnetic north. It is usually obtained from the local maps.

Calibrating the compass tells the compass that magnetic north=true north so you don't have to manually adjust for declination for where you are diving

Disagree: A digital compass does not know where true north is unless you tell it. It cannot determine that value on its own. You really do not have to compensate for declination when diving unless you are following a map that is plotted using 'true north' coordinates

 

[tbone1004]

Agree: Declination is both the magnitude and direction of the difference between true north and magnetic north. It is usually obtained from the local maps.



Disagree: A digital compass does not know where true north is unless you tell it. It cannot determine that value on its own. You really do not have to compensate for declination when diving unless you are following a map that is plotted using 'true north' coordinates

aren't most maps plotted using true north coordinates?

I guess I missed some info. The Shearwater has you calibrate by spinning around to make sure it isn't being interfered with by any EM fields or anything, but it does also ask you what your declination is and I lump that in with part of calibration since it's on the same menu

 

[npole]

The north on the maps is the the geographical north, the compass will give you the magnetic north; you need to enter the declination manually because it cannot be calculated (the calibration will only calibrate the compassi.. it cannot calculate the declination).

 

[WatchTryst]

Like a few others here I just use the Perdix compass. My oil compass stays in the dive bag.

 

[lowflyer]

The Perdix compass is great. It's quite sensitive, and unlike an oil filled magnetic compass, it doesn't have to be held perfectly level to be accurate. Obviously it needs to face the direction you are going, but less concentration in keeping it level is needed.

 

[lowflyer]

I am lost.

I don't see where the calibration and definitely not the declination setting matters. And that latter is all I have really used my compass for. Either, take a heading away from the shore, to be sure I can swim back to the shore without surfacing, or, take a heading from the anchor line along the wreck, so that if I get turned around, I can check my compass to have an idea of which way to swim along the wreck to find my way back to the anchor line.

I know what you are saying and don't completely disagree, but consider this true scenario. An instructor leading a class with me tagging behind surface swam out to a buoy below which was a platform. The class descended, did some skills and then swam around. The instructor then wanted to head back to shore, which was in a westerly direction. I'm following and wondering why the instructor is going south. At some point he sees that something is messed up and looks at me. I point to the west, but now we really need to go northwest to reach shore. Problem: the instructor has a Perdix and had changed the battery without re-calibrating the compass. Moral of the story: that compass can be off quite a bit if not calibrated, and sometimes it is important to have accuracy.

 

[Charles2]

aren't most maps plotted using true north coordinates?

Orienteering maps are usually gridded using magnetic north instead of true north. There may be others.

 

[Scared Silly]

People who have the Perdix/Perdix AI, how do you feel about the compass? Do you have another non-digital compass that you dive with?

For years I used and analog compass. It worked great until it cracked. I got a replacement which cracked putting it into the bungee mount. I tried another which also cracked. At that point I sold my Petrel 1 and got a Petrel 2 with the compass. I have not looked back since.

FWIW I have tried some of the other digital compasses such as those on Suunto computers. I disliked them because of the graphics. I actually dislike the graphics on the newer computers. The algorithm was fine as were the graphics on the older versions. That is when I bought the Petrel.

Regarding the calibration and declination. You always calibrate. If you see something and take a compass reading to get there one does not need the declination. If one uses a map, you need the declination.