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about pocket transits
A pocket transit compass is often simply called a "Brunton"
The history of the Brunton pocket transit starts in 1894 when the original design was patented by a Canadian geologist named D.W. Brunton as a rugged, simple instrument for basic field mapping in remote areas. For over 75 years it was made with his name on the label by the William Ainsworth Company in Denver, Colorado. The instrument nameplate read "D.W. Brunton's (trade mark reg. U.S. pat. off.) pocket transit". Because of that long association of the name Brunton with the pocket transit, most field geologists simply refer to the pocket transit as a "Brunton". As time has passed and geology as a field profession has declined, we now find customers sometimes asking us for a "Bunton" compass, or a "Bruton" compass.
After the original patents expired, many other companies produced almost identical instruments sold under their own company names. Now, "Brunton" is actually a trademarked name that belongs to the Brunton Company in Riverton, Wyoming, and should only be applied to a pocket transit made by them. There was even a time when some of the pocket transits sold by Keuffel and Esser, the former slide rule, drafting equipment, and instrument maker, were actually produced by the Brunton company for K&E.
You can usually find several non-Brunton pocket transits on the market, including polished brass models from India made for collectors, and others from Germany, China, and Japan made for use by geologists. Our opinion is that you need to evaluate these individually to make certain that one will meet your needs for function and quality.
Since 1972, genuine Brunton pocket transits have only been produced by the Brunton Company in Riverton, Wyoming, which bought the tooling and name from the former Denver Ainsworth operation.
In 1996 Silva Production, AB of Sweden, the world's largest compass manufacturer, acquired the Brunton company. Silva has has continued the Brunton name and tradition of the pocket transit.
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Why, after 100 years, are pocket transits still being made?
The pocket transit design has proven to be extremely rugged and versatile. We have heard from a retired Canadian mining engineer who reports that his 62 year old Brunton, serial number 38445, is still in great shape. Minus a bit of spotting on the mirror, but that is after a career of exploration and development work, and recreational camping and hiking use after.
But because modern surveying is now done with a range of electronic instruments that are fast and precise, you wouldn't think there would still be a need for geologists to use a Brunton pocket transit. The reason for its survival in the electronic age, is that in addition to its rugged field compass, the Brunton contains an accurate inclinometer mechanism.
The compass and inclinometer are the tools by which measurements of strike and dip of geologic structures are made. So, no matter how many advances are made with laser surveying instruments or GPS systems, there are some measurements that a field geologist will always need to do using judgment and skill, with a Brunton Pocket Transit.
In geology, the pocket transit is a symbol of the profession. We occasionally sell a replacement Brunton pocket transit to a geologist who hasn't actually used one in the field for years, but can't find their original but doesn't feel fully equipped without it.
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How to Select or buy a Brunton pocket transit for geology studies
There are several models of the Brunton pocket transit made for geological use. We stock their six most popular models, and can special order the others when a customer needs one.
They are functionally almost identical, and include: needle lift mechanism to lift the needle off the pivot when the case is closed; magnetic damping of the compass needle to speed up readings; bubble level to assure the case is being held horizontally for accurate readings; inclinometer with bubble level for dip measurements; gear driven magnetic declination adjustment, and four of them have waterproof/dustproof construction. Any Brunton is a great instrument. These six possibilities just allow you to tailor one to suit your own preferences. Here's how Kooter sorts them out:
First, decide how much attachment you have to tradition.
The "2000" or "Commercial" series is the closest to the original design in having the traditional aluminum body without either waterproofing or dust proofing features. The needle is a conventional high center of gravity design, which makes it a bit particular about needing to be factory balanced for use in a specific location in the world. They are only about $30.00 less in cost than the waterproof version, so most people opt for the waterproofed LM version.
The "LM" or "International" series is an early 1980's evolution of the pocket transit. It retains the traditional machined aluminum body, but incorporates seals to make it water and dust proof. The needle pivot has been changed to a lower center of gravity so it is more forgiving about being taken to other locations without needing special balancing. For that reason the balance is called "International", and we will explain the limitations to that term later.
The "ComPro®" models are a late 1980's major design change. We used to think of this as a "new" design, but now we realize that it has been out there so long that for many of our customers this was the first Brunton they ever saw, so for them it is just as traditional as the aluminum body is to us.
The ComPro was designed from the ground up to take advantage of modern materials including a molded composite body that reduces weight, and very powerful magnetic materials. The results have been very good for the user. The cast magnet is very rugged, and smaller in diameter. This allowed the bubble levels to be re-located for better visibility. The needle also settles out or "damps" faster. The composite used for the body has proven to be not only rugged, but also dimensionally stable over time.
The ComPro uses the same construction which Brunton uses for the M2 version supplied to the military. In it's early days it also carried the name "International", which we guess indicates it might have been the first Brunton to have that feature.
The GeoTransit became available about 2001. It's design is based on a very efficient method of rapidly taking geological strikes and dips. In use, the bottom of the body is held horizontal by the use of level vials on the sides of the body. The hinged upper lid is then brought into contact with the geologic formation being measured. Then, the locking pin of the needle is depressed, which in the Geo Transit unlocks the needle. After the needle has damped out, the pin is released and the needle is locked in the strike direction. Then, the geologist can move the compass so the dip can be read on the prortractor of the lid hinge, and the strike bearing of the locked needle can be read.
The Geo Transit is a very rugged instrument with a lifetime warranty from Brunton.
Degrees or Quads?
Second, decide whether you want your Brunton to have a dial marked in units of "quads", or "0-360 degrees". If you don't personally have a preference as to which dial you want, check with a professor you will be studying with for their suggestion.
Some people call a degree compass an "azimuth" compass. We use Brunton's "quads" and "degrees" terminology to avoid confusion, because that is how they mark their cartons. But if you use the term "azimuth compass" it is OK with us, and we will understand that you mean the one that isn't "quads".
Third, figure out whether your geological activity is in the Northern or Southern hemisphere. In the Northern hemisphere, the magnetic dip tries to pull the north pointing end of the needle downward, so the factory adds a tiny bit of weight to the south pointing end to make the needle balance properly. But if you are in the Southern hemisphere, the weight needs to be on the north pointing end of the needle to compensate for the magnetic dip that tries to pull the south pointing end downward.
In reality a compass can only be perfectly balanced for one specific location around the globe. But, depending on the needle suspension, the compass can handle a range of magnetic dip. Both the LM and ComPro models we stock have "International" needle suspension, meaning that within limits, it can accommodate a limited amount of variation in magnetic dip without any trouble. But there are limits you need to keep in mind. In general, the term "International" best describes the ability to handle variation of dip that happens as you change longitude.
A stock Brunton is made for the Northern hemisphere, so if you are going to use a Brunton very near or south of the equator, let us know and we will special order a compass balanced to account for your region.
The factory does not charge for this special balancing if it is done when the compass is ordered, but there is a service charge if you need to do it later.
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User's Instruction Manuals for the Brunton Pocket Transit and Geo Transit
We have only seen printed instructions detailing the use of the pocket transit for geological mapping in long out of print geology textbooks. Most field methods of the use of the pocket transit for structural geology are now passed down from instructor to student during geology field methods courses.
Replacement paper copies of the user instruction manuals now supplied by Brunton with the pocket transit and Geo Transit are available from the factory. There is a nominal charge of about $5.00 for postage and handling. Contact Brunton customer service at 1-800-443-4871 for current pricing and ordering information.
You can download and save Adobe PDF files of these factory manuals from our website. You will need to have the free Adobe Acrobat Reader software installed on your computer to view or print the files. These PDF files are essentially photographic copies of the paper version in their printedl 4-1/4 x 4-1/2 inch format. You can print the pages on your printer, but there will be only two pages printed on each of your 8-1/2 x 11 inch printer paper.
Each file is about 1 MB in length, so may take several minutes to download depending on your internet connection speed.
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You can Buy a Brunton pocket transit from Kooter's Geology Tools
Last revision 05/20/2013