Compass declination

[stefan]

Hello,
I am from Romania and am thinking of buying a Brunton SurveyMaster from the US. There is just one problem. I guess it comes calibrated for the region it will be used in. Can I change the magnetic declination in some way to be the right one in my country ?

The same question comes with the SUUNTO Tandem instrument. Can it be recalibrated by anyone or does the calibration have to be done by specialists?

Thanks in advance

[NZcaver]

I am from Romania and am thinking of buying a Brunton SurveyMaster from the US. There is just one problem. I guess it comes calibrated for the region it will be used in. Can I change the magnetic declination in some way to be the right one in my country ?

The same question comes with the SUUNTO Tandem instrument. Can it be recalibrated by anyone or does the calibration have to be done by specialists?

Hi Stefan. Do you mean magnetic declination, or magnetic dip?

Declination shouldn't matter, because as far as I know most (all?) modern cave surveying uses magnetic bearing azimuth values with no adjustment. Any conversion from magnetic to true can be done later on the computer, when you enter your raw data into a mapping program. Unlike many basic "Boy Scout" type compasses, Suunto survey instruments don't even have a declination adjustment and I don't think Brunton's do either.

Regarding the magnetic dip issue, if my geography is correct Romania and the US are in the same world magnetic region (Region 1). So any surveying compass designed for use in the US should work just fine for you. See this map:



Each magnetic region relates to how much the compass disc will dip downwards when pointing north. When a compass is assembled by the manufacturer, tiny weights are added to balance the disc to a neutral position. You can generally use a compass balanced for a different region with good accuracy, but you may have to tilt the whole compass up or down slightly to make the disc spin freely. It's not ideal, but it should work. Suunto compasses are built region-specific and can't be changed without having the whole disc enclosure replaced (which probably costs the same as buying a whole new compass). I assume the Brunton units can't be changed either.

[stefan]

Hi and thanks for the fast reply.

Yes, the magnetic declination was the one in my question. I did not now anything about the dip and the effects it has, so thank you for explaining it.
So the instruments like the ones I mentioned point to the magnetic north without any correction !!!? That's great news !

Thank you for your help.

[NZcaver]

You're welcome.

Shooting simple uncorrected magnetic bearings azimuths is standard practice when surveying caves. If you try to correct for declination while in the cave, there's a good chance of introducing significant errors into your survey data.

Happy surveying.

[Tlaloc]

...magnetic bearings is standard practice when surveying caves...

A bearing is an angle from zero to 90 degrees east or west of north or south. An azimuth is an angle greater than or equal to zero and less than 360 degrees (or other units of angle) clockwise from north. Almost all compasses used in cave surveying are marked in azimuths.

[Dwight Livingston]

A bearing is an angle from zero to 90 degrees east or west of north or south. An azimuth is an angle greater than or equal to zero and less than 360 degrees (or other units of angle) clockwise from north. Almost all compasses used in cave surveying are marked in azimuths.

I don't think you can apply those definitions universally, especially for "bearing." Check out http://www.answers.com/topic/azimuth?cat=technology.

[Tlaloc]

So my definition of an azimuth is correct. Answers.com also agrees with my definition of bearing:

http://www.answers.com/bearing?cat=technology

"4. In surveying, the horizontal angle between a line and a reference meridian adjacent to the quadrant in which the line lies."



Bearings are used in land surveying but almost never in cave surveying.

[NZcaver]

...magnetic bearings is standard practice when surveying caves...

A bearing is an angle from zero to 90 degrees east or west of north or south. An azimuth is an angle greater than or equal to zero and less than 360 degrees (or other units of angle) clockwise from north. Almost all compasses used in cave surveying are marked in azimuths.

Good point - I could have used the term "azimuth" in that context. But since we're being pedantic, your definition of "bearing" is not strictly true in reference to modern navigation and surveying.

In simple terms, a compass bearing is generally accepted as being the direction from one point to another as determined by a compass. For example, "beacon sighted, bearing 3-1-0 degrees." This compass bearing can be standardized relative to true north, or magnetic north. It can be measured in degrees (up to 360), mils (up to 6400), grads (up to 400), or using other more obscure scales. It can be taken on land, at sea, or in the air - or underground.

You seem to be thinking of the old quadrant system of bearings (eg "S 70 W" being 70 degrees west of south), which is now a long-outdated system. As I understand, for all practical purposes over the last hundred years or more, compass bearings have referenced a full circle and not just a quadrant. Anybody older than that can probably be excused for still thinking in quadrants.

And since we're quoting references:

Compass bearing (from answers.com) - (navigation) Direction relative to north as indicated by a compass

Bearing (from yourdictionary.com) - direction relative to one's own position or to the compass

Although it's my contention the terms bearing and azimuth are practically interchangeable in modern navigation and surveying, I have edited my previous posts to appease the experts who may cringe at the word "bearing" being used in this context.

[Tlaloc]

Good point - I could have used the term "azimuth" in that context. But since we're being pedantic, your definition of "bearing" is not strictly true in reference to modern navigation and surveying.

Navigation has nothing to do with it and my definition of bearing and azimuth ARE strictly speaking, exactly right.

You seem to be thinking of the old quadrant system of bearings (eg "S 70 W" being 70 degrees west of south), which is now a long-outdated system. As I understand, for all practical purposes over the last hundred years or more, compass bearings have referenced a full circle and not just a quadrant. Anybody older than that can probably be excused for still thinking in quadrants.

You are absolutely wrong since all metes and bounds descriptions (legal descriptions of property) are described in bearings and that's why survey compasses like Bruntons are still manufactured in bearings today. As far as the this is an obsolete 100 years ago thing, you totally made that up to make it sound like you know what you're talking about but to anyone who is a surveyor it actually flaunts your ignorance.

Although it's my contention the terms bearing and azimuth are practically interchangeable in modern navigation and surveying, I have edited my previous posts to appease the experts who may cringe at the word "bearing" being used in this context.

You are absolutely wrong. Navigation has nothing to do with it, it's a red herring in this discussion and bearing and azimuth are NOT interchangeable. When someone who is obviously a professional in the field points out that you are completely wrong and rubs your nose in the documentation you should admit you are wrong instead of claiming to be an expert in the field and another irrelevant one (navigation - straw man) an making up a whole bunch of excuses to demonstrate why you were right.

This is how people debate on the Internet today: obfuscate, denigrate, change the subject, use an argumentum ad hominem, a straw man or a red herring but NEVER, NEVER admit you are wrong. Also always have the last word, which you will now ad:

[Bob Thrun]

Hello,
I am from Romania and am thinking of buying a Brunton SurveyMaster from the US. There is just one problem. I guess it comes calibrated for the region it will be used in. Can I change the magnetic declination in some way to be the right one in my country ?

Why buy from the US? The SurveyMaster is made in the Silva factory in Livingston Scotland. Why ship it across the Atlantic twice? The instrument is sold under the Brunton brand in the US because Silva Sweden does not own the Silva trademark in the US.

All the cave survey data reduction programs have a provision for magnetic declination. I have seen data sets there the wrong declination was used on the compass. Correcting the correction is a mess. The best thing is to keep the declination correction always set to zero.

Suunto makes a compass that has a declination adjustment. It does this by sliding a thin sheet of transparent plastic with a ssecond hairline in front of the compass capsule. The space between the sheet and the capsule provides a place for water and mud to collect. The problem with having two hairlines visible should be obvious. As I recall, the adjustment range is plus or minus 7 degrees. This is not enough for my caving area.

[NZcaver]

You are absolutely wrong. Navigation has nothing to do with it, it's a red herring in this discussion and bearing and azimuth are NOT interchangeable. When someone who is obviously a professional in the field points out that you are completely wrong and rubs your nose in the documentation you should admit you are wrong instead of claiming to be an expert in the field and another irrelevant one (navigation - straw man) an making up a whole bunch of excuses to demonstrate why you were right.

I stand corrected.

It was not my intention to make navigation a red herring or straw man in this discussion. I've always equated navigation and surveying as being similar beasts in many ways, but obviously professionals like yourself know better. I've never claimed to be an expert in either field. Perhaps our different nationalities account for our differences in techniques and terminology, and it's also quite possible I've received some misguided information over the years.

Anyway, thank you for pointing out the error of my ways and for kindly rubbing my nose in your documentation.

This is how people debate on the Internet today: obfuscate, denigrate, change the subject, use an argumentum ad hominem, a straw man or a red herring but NEVER, NEVER admit you are wrong. Also always have the last word, which you will now ad:

Yes, internet debates can rapidly turn nasty sometimes - even with such benign subjects like cave surveying. After casting such accusations, perhaps one should pause for a moment to take a quick glance in the mirror.

Apologies for disseminating false information about bearings, and for upsetting you with my earlier comments.

[stefan]

Why buy from the US? The SurveyMaster is made in the Silva factory in Livingston Scotland. Why ship it across the Atlantic twice? The instrument is sold under the Brunton brand in the US because Silva Sweden does not own the Silva trademark in the US.

Well, the only reason was that i didn't know about Silva. I just heard about Brunton and I thought this was the actual original brand of the SurveyMaster. Thanks for the tip. You are absolutely right about the Atlantic crossing part

[danstraley]

I'm reading an interesting thread until I run across our little wannabe Aztec Warrior apparently suffering from Napoleonic Syndrome. Although I can appreciate his quest for accuracy, I see no provocation for his tone of being a total jerk. Everyone's a tough guy on the net.. It might be OK to act like this when arguing about whether Captain Kirk beefed green aliens on your Star Trek message boards, but this is a caver forum, and it's not appreciated.

Good point - I could have used the term "azimuth" in that context. But since we're being pedantic, your definition of "bearing" is not strictly true in reference to modern navigation and surveying.

Navigation has nothing to do with it and my definition of bearing and azimuth ARE strictly speaking, exactly right.

You seem to be thinking of the old quadrant system of bearings (eg "S 70 W" being 70 degrees west of south), which is now a long-outdated system. As I understand, for all practical purposes over the last hundred years or more, compass bearings have referenced a full circle and not just a quadrant. Anybody older than that can probably be excused for still thinking in quadrants.

You are absolutely wrong since all metes and bounds descriptions (legal descriptions of property) are described in bearings and that's why survey compasses like Bruntons are still manufactured in bearings today. As far as the this is an obsolete 100 years ago thing, you totally made that up to make it sound like you know what you're talking about but to anyone who is a surveyor it actually flaunts your ignorance.

Although it's my contention the terms bearing and azimuth are practically interchangeable in modern navigation and surveying, I have edited my previous posts to appease the experts who may cringe at the word "bearing" being used in this context.

You are absolutely wrong. Navigation has nothing to do with it, it's a red herring in this discussion and bearing and azimuth are NOT interchangeable. When someone who is obviously a professional in the field points out that you are completely wrong and rubs your nose in the documentation you should admit you are wrong instead of claiming to be an expert in the field and another irrelevant one (navigation - straw man) an making up a whole bunch of excuses to demonstrate why you were right.

This is how people debate on the Internet today: obfuscate, denigrate, change the subject, use an argumentum ad hominem, a straw man or a red herring but NEVER, NEVER admit you are wrong. Also always have the last word, which you will now ad:

[Dwight Livingston]

Tlaloc provided me a reason to do some reading on the subject, which I appreciate, and in the context of surveying I think he is largely correct. You could make some quibbles about azimuths occasionally be taken from south rather than north, but I agree that his point, strictly in a survyors context, is right. In the future, should anyone tell me about an azimuth of 51 degrees, in most cases I think I can safely assume what they mean. If they tell me about a bearing of 51 degrees, some discussion will follow.

In a larger context (and not much larger) bearing and azimuth are interchangable, and I expect I'll continue to use them that way. I certainly wouldn't quibble with anyone else's use of bearing to mean direction.

[George Dasher]

I thought NZcaver's posts were very good, and I was particularly impressed by his first post. I was going to comment on the original thread, but I thought, "What is the point? NZcaver has covered all the details, and he has even included the appropriate map."

Also Bob Thrun has a good point. "Why order a compass from the US, when you can get it from Britain?"

As far as the azimuth-bearing thread: Tlaloc could have been kinder in his reply.

Perhaps quadrangle bearings are still in use, but it is also true that you don't see them as much as you used to. The problem, simply put, is that it is easy to confuse the quads, whereas this is not possible with the other method (whatever you choose to call it).

I use the term "bearings" to describe quadrangle bearings and the term "azimuth" to describe directions between 0° and 360°. I know this many not be 100% correct, but I feel that it is the modern trend. And besides, it is a simple designation.

Also, quadrangle bearings are used to describe the direction of planes (such as with geological strata or structures), as these planes are actually two directions, not one.

And as far as magnetic declination is concerned, it is always easier to adjust this when reducing the data, rather than worrying with it in the cave. Or just rotate the final map, if you drawing by hand and it is a small cave.