Why north at 180 degrees?

[Pearldiver07]

I'm not really sure where I said my military experience had or would cause confusion handing a compass.

I believe I was trying to make a point that a LARGE portion of people out there don't know how to use a compass or know the fundamentals of navigation, including those who teach the skills.

The way you wrote your post, I'm surprised that it took you leaving the military to finally learn how to correctly use a compass. I must remember that REMF's play a valuable role in combat operations.

I knew very well how to use a compass in the military. Apparently I didn't state that original post clearly enough. That instructor that I referenced was an infantry SFC at 7th Infantry Division (Light)'s Primary Leadership Development Course (PLDC). I was a young upstart of a buck seargent at the time.

 

[paddler3d]

Sorry for the confusion. What are the chances.

 

[SelkieDVM]

Thanks all again for the responses. As it happens I do know how to use a compass, even what declination is and how to adjust for it. I had just never taken a specific bearing with a scuba compass, and so had not noticed that the bearings as seen looking down were in opposition to other compasses I had used. Not using the window, I just didn't put two and two together. Recently on a sailing trip, the comment was made that the boat's binnacle compass had not been calibrated, so I got the scuba compass out just to compare and noticed the difference.

 

[scjoe]

It looks like some divers who only use scuba compasses didn't know as much about compasses as they thought and weren't aware of this flip flop either or that would have been the first answer you got.

 

[mrfixitchapman]

Sorry for the confusion. What are the chances.

Probability = 1


DC

 

[MauiScubaSteve]

It looks like some divers who only use scuba compasses didn't know as much about compasses as they thought and weren't aware of this flip flop either or that would have been the first answer you got.

Well since I was the first answer SelkieDVM got, I'd like to address the OP;

Just curious...

Why does my dive compass (as well as a few others I've noticed) have north set at 180 degrees rather than zero like the ones I've used for hiking and sailing?

Following a long tradition on SB, I questioned the acknowledged Divemaster's training and also posted this picture;

​

Obviously, that question has been answered. Not answering the question that was not asked is not a sign the non-answerer did not know the answer.

 

[Steven Taylor]

Whether this is a real post or not, I will respond, because that's what I asked my OW instructor when I got certified and he couldn't respond. This question has also come up in several classes that I have DMed.

If you're familiar with land navigation as with hiking and camping or in my case the Army, you may be used to compasses that have the needle mounted on a disk that has the various degree headings.

On this type of scuba compass, you do not read the degree numbers on the disk from the top. The numbers on the disk are for reading only through the window on the back. So, if you're headed towards 0 degrees, the disk will read 180 on the top, but 0 from the back. In other words, all the numbers read from above at the front will be opposite from those read from the back.

You use the top part of the compass by setting your heading with the numbers on the bezel and turning the direction you are facing until the 0 mark lines up with the North mark not the 0 on the disk.

To simplify things, I just tell the students to look through the back window and forget using the top degree markings until they take AOW.

Very helpful answer. Thanks. I just bought a compass in preparation for an Advanced Open Water course starting in a few weeks time and I was wondering why North was at 180 degrees.

 

[tracydr]

Thanks all again for the responses. As it happens I do know how to use a compass, even what declination is and how to adjust for it. I had just never taken a specific bearing with a scuba compass, and so had not noticed that the bearings as seen looking down were in opposition to other compasses I had used. Not using the window, I just didn't put two and two together. Recently on a sailing trip, the comment was made that the boat's binnacle compass had not been calibrated, so I got the scuba compass out just to compare and noticed the difference.

I asked the exact same question when I was at the start of my DM course. I used to organize the Expert Field Medical Badge Training for my medics twice a year and would help sometimes with navigation.
I found the underwater compass very confusing be causing it was backwards from a " real" compass.

 

[billt4sf]

I've even found that most folks have no idea that there are actually three Norths out there: True North, Magnetic North, and Grid/Map North.

Not to confuse things further, but -- geographic north is actually magnetic south.

 

[captain]

Go get one of these. If you want you can just cut the base plate down to a circular shape that will fit into your console. Make a white plastic disk ,(I made one from a cottage cheese container lid), to go under the compass. As long as you have a liquid-filled compass it will work just fine. I have one zip-tied to a slate, too.

DC

That is the only compass I have ever dived with, cheap and works great. No need to spend big bucks on a "divers" compass.