A Trimble is great but field archaeologists still use a compass 2

Compasses are central to archaeological fieldworkOne of the most controversial blog posts I’ve ever written discusses a situation where a former co-worker and field tech had to teach their PhD supervisor how to draw a plan map. Many commenters told me it wasn’t a PhD’s job to know how to do the work of a field tech. I argue that they should have learned that stuff before they even made it to the PhD level. I understand universities cannot teach students everything but I strongly believe any quality undergraduate archaeological field school should have showed each student how to draw a plan map.

In that post, I discussed how I also once had to teach a former supervisor with a PhD how to use a compass to set shovel probe transects in the forest because they had only previously done this using a Trimble hand-held GPS unit (I still don’t know how they were able to set up arrow-straight probe transects using a Trimble).

We were in the forest and the Trimble was struggling because of the trees and hills. Naturally, the crew all pulled out their compasses and sat back, drinking coffee in the rain, waiting for the boss to get things going. After a few minutes, I realized somebody needed to act because we were burning daylight. It was only then that I learned our supervisor did not know how to use a compass and was waiting to get enough satellite coverage to set up the probe transects using the Trimble.

Even though I wasn’t in charge, I realized my job was on the line. All of ours were. We couldn’t wait for Space Age technology. We’d have to use some good ol’ 19th century tech.

None of us knows how to use a compass when we’re born

At the time, I didn’t care what degree this person had. I was more concerned with getting the job done on time and on budget. Politely, I asked how I could help and learned that the supervisor didn’t know how to use a compass. I also learned that they didn’t have a proper compass (the one they brought into the field was more suitable to Boy Scout orienteering than doing archaeological survey in the forest). So, I let the supervisor use my compass and gave a really quick crash course in land navigation using a map and compass.

Teaching field technicians and field school students how to properly use a compass in the field is something I’d done before in the past. It was no big deal to teach my supervisor the same skills. I cannot recall how many hours I’ve spent in the field teaching other archaeologists how to use a compass. This work was mainly done for selfish reasons: I needed all my co-workers to know what they were doing so I would look good doing my job. It was also done because, in the distant past, somebody taught me everything I know about using a compass so I felt like I was just paying it forward.

Growing up as an outdoorsy boy from Idaho, I learned how to use an orienteering compass in elementary school. In the 1990s, orienteering was part of PE in Boise, Idaho so I learned the basics of setting a bearing and walking a transect as a boy. Later, as a teenager and twentysomething, I started applying these compass skills to topographic maps while backcountry hiking. Still later, as an archaeologist, I learned how to use a compass and tape to draw site maps.

I was only able to gain these skills through patient mentorship and steady application. But, we don’t all get a patient mentor. In fact, few of us get mentors at all. Nevertheless, field archaeologists are expected to be able to use a compass from their first day on the job. Few of us can do that on day one. It is my hope that this blog post helps.

It doesn’t matter how you learn how to use a compass. The only thing that matters is that you know how to properly use a compass.

REI can teach you how to use a compass

I’ve frequently pondered making a “How to Use a Compass” video for this blog but I didn’t have the video production capabilities. Fortunately, I don’t need to make that video because REI has created one for us. This short video shows you the basics of using a compass with a topographic map. I couldn’t have taught it better myself:

In addition to creating a “How to” video for using a compass, REI has also made a video demonstrating how to read a topographic map. It may seem crazy but I’ve also spent a fair amount of time showing co-workers, field techs, and students how to read a topographic map. The REI video is simple and the same basic concepts apply whether you’re reading an architectural drawing of an area of potential effect (APE), a road map, or a map created by your company:

(NOTE: Make sure the field maps your company makes for you to take out into the field also include a UTM grid adjusted for magnetic declination that you can use with your compasses in the field. Politely tell your mapping person/department that your field maps MUST have the grid overlain. It’s best if the UTMs are adjusted from true north to magnetic north so you can easily use your compass with the company maps If the UTMs are simply projected upon the map, you need to adjust some of the lines using a protractor and ruler to account for the magnetic north your compass uses.)


Drawing a field map using a compass

Okay. You know how to find your way use a compass and map. But, how do you use the compass to create a map?

This video created by teacher Matt Tiller of the Verona School District in Wisconsin does a pretty good job of explaining how you make a version of an archaeological site map using a compass and measuring distances using your pace. Tiller’s second video shows how you can use your compass bezel like a protractor to calculate directions. It is very similar to how I was taught to make a pace map of my orienteering area as an elementary school student.

Being able to transfer information taken in the field to a paper map is foundational to drawing an archaeological site map with hand tools because you need to be able to gain proficiency at translating field data into representational data like a map:

My friend Chris Webster also created a pretty good mapmaking walkthrough on the DigTech blog. These two posts and Mr. Tiller’s videos are a “must-read/see” for any up-and-coming archaeologist that doesn’t already have these skills:

#95 Shovelbums Guide Part 16.1: Pace and Compass Maps

#96 Shovelbums Guide Part 16.2: Pace and Compass Maps

Drawing a map using hand tools is a very hands-on activity that is best learned by doing. These resources are a good start but you will need to practice in order to build competency at drawing field maps. But, you have to have a compass in order to get started.

What kind of compass should you get?

Any compass with a clear baseplate and movable bezel will do. However, it will be more difficult to do all the things you need for archaeological fieldwork without a sighting notch and mirror. Also, your co-workers will probably think you’re an amateur if you show up with an orienteering compass (i.e. the one they mostly showed in the REI videos) so get a professional one.

Since I started doing archaeology, I’ve only used one model of compass in the field: The Silva Ranger (http://store.silvacompass.com/military-compasses-professional-compasses). Reliable, durable, and inexpensive (usually only about $50), the Silva Ranger is my field compass of choice. I’ve owned several Rangers over the years and cannot recall the hundreds of hours of fieldwork my Ranger has been through. I like the Ranger but that doesn’t mean there aren’t other excellent field compasses. Suunto makes some excellent navigation compasses with mirrors (http://www.suunto.com/en-US/Product-search/See-all-compasses/). The Brunton TruArc is also good (https://www.brunton.com/search?type=product&q=truarc).

The brand is not as important as the compass’ features:

  1. You need a movable bezel. This is not an option. Even Boy Scout orienteering compasses have this feature.
  2. A clear baseplate with inch and centimeter rulers is also a necessity. You will need this for drawing maps as well as determining bearings from field maps.
  3. Adjustable declination is a near necessity as well. This way you don’t have to keep doing math in your head to keep your bearing straight.
  4. A sight and mirror is also a near necessity. This makes it easier to determine which direction you should be walking.

You shouldn’t pay more than $100 for your compass unless it’s an emergency (i.e. you’re in rural Montana and the only thing you can find is an overpriced Silva Ranger at a fly fishing store). You do not need a pocket transit. If your project needs that much accuracy they should be using a total station in the field. I am also wary of using a sighting compass because you can’t really use it to draw maps. Sighting compasses don’t have a clear baseplate so you can’t do all the stuff Mr. Tiller shows in his second video. You should not rely on using your smartphone’s compass because it isn’t accurate enough for professional work. It’s okay to use the phone to figure out a rough direction but field maps and transects shouldn’t be made with an iPhone.

In addition to a compass, you will need a pencil, a ruler marked in inches and centimeters, a protractor, and a calculator (Your phone will suffice as a calculator in this case, especially if it has some scientific functions). Field navigation does require some accuracy and a little bit of geometry. The 3-inch ruler on your compass baseplate isn’t enough to mark long transects or features on the map, which is why you will need a ruler. A 10-centimeter section of a broken Rhino Folding Ruler will suffice for most map work. Your tape measure will do but it’s better to have a ruler as your straight edge. The protractor is primarily for drawing site maps. You won’t be using it on every single project but it behooves you not to have one in your field kit.

When to get a new compass

While it is common to have a compass for several years, it’s not unknown for compasses to get mucked up. We use these devices frequently in the field. Eventually, your compass will fail. Here are some common reasons why you will need to buy a new compass:

There’s a bubble in the bezel. A bubble will interrupt your magnetized needle making it inaccurate. That’s not good.

The bezel no longer rotates. Dirt destroys archaeology equipment. It can clog your compass’ bezel. Most of what we do with a compass depends on being able to adjust that bezel. If you can’t do that, you can’t do what you need to do in the field.

You can’t read all the numbers on the ruler. Or, the corners of the baseplate have been rounded so much that the first few millimeters aren’t there anymore. Your device is no longer measuring accurately at this point, which makes you have to rely on your ruler. If you have to use other tools to get your tool to work properly, it’s time to start thinking about getting a new tool.

Another magnet has “demagnetized” your needle. Other magnets, like the magnetic clasps on a backpack, will change the magnetism of your compass needle so it doesn’t accurately point north anymore. I am unaware of any fix for this so just get a new compass (NOTE: Your compass will not measure accurately if you are standing next to a large piece of metal [like a work truck] or working under high-voltage power lines. Before you throw away your compass, make sure it’s not being effected by something in your work environment.)

You just started doing archaeological fieldwork. Get a compass ASAP if you do not already have one. Don’t be that guy/gal/person.

Get a compass. Start using it.

If you’re an archaeologist who remembers the time before hand-held GPS units (like the 1990s), you’re probably as adept at using a compass in the field as John Rambo (NOTE: Don’t use a Rambo-style, compass on a commando knife in the field. You will be the brunt of many jokes for decades to come if you bring that sh*t). I’ve become increasingly aware that many young archaeologists do not know how to use a compass in the field. Fortunately, this is not a difficult thing to learn.

If you don’t know how to use a compass, the first step is to get a decent, archaeology-grade compass. Second, you need to start using it. Begin by using the compass to set bearings you can walk towards. You will also have to determine your pace. This can be done by counting your steps as you walk along a tape measure or on a football field. After you’ve determined that, move up to using your compass with road maps or topo maps. Once you’ve learned how a compass works and applied some of these basic principles, you can move on to drawing maps using a compass, a ruler, and a protractor. You’re completely ready for navigation in the field if you can do all of these things.

What did I miss? What else do you need to know about using a compass in the field? Tell me by writing a comment below or send me an email.


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2 thoughts on “A Trimble is great but field archaeologists still use a compass

  • Joe Sixpack

    1. A compass is not “19th century tech”. It’s been around since before 500 BC.
    2. Why would anyone break a Rhino foldable tape measure to use as a straight edge???
    3. A compass is definitely not necessary in archaeology anymore, no matter how much anyone tries to spin it. PhDs don’t know how to use it because they don’t NEED to use it. Trimbles are there to replace a compass.
    4. A bubble is necessary in a compass as it helps level the compass. I’d expect anyone who claims to have used a compass for years to know that bit of information.

    • SuccinctBill Post author

      I have to first thank you for reading the blog post and submitting a comment. Writing a comment and going the extra mile turns a static post into a discussion, which is what I always like to see. Here are my responses to your comments:
      1) You are correct about the origins of the compass. I guess I was not clear in what I meant by compass but I was specifically addressing the liquid-filled, hand-held bearing compass featured in the REI videos and my blog post. This sort of compass is an amalgamation of inventions and evolution in compass technology that took place in the 18th and 19th centuries. By WWI, the earliest renditions of the orienteering/bearing compasses we use in archaeology were in use by most armies. Compasses had been around for centuries but the ones we use in the field came into use during the late 19th century.
      2) Nobody means to break a plastic Rhino ruler but it happens if you use it enough. Rather than toss the ruler after it’s broken, I keep some of the broken sections of the ruler in my field kit to draw maps and calculate bearings. Those little sections are really useful because they come in metric/inch intervals on each side which makes it easier to draw a map on graph paper than if you use the complete Rhino. If you haven’t broken a Rhino, just use the ruler as is.
      3a) I disagree with the necessity of using a compass in the field on several levels. A Trimble is expensive so its unlikely everyone on the survey line is going to have one of their own. You need some way to accurately establish walking transect lines in open places like the American West. Also, a Trimble is not going to allow you to set a bearing the same way a compass will because your location dot/arrow jumps around from time to time as the GPS switches between satellites and reception quality. With a compass, you just have your crew set the bearing, establish their own point on the horizon, and everybody walks in the same direction until you reach your desired destination or you find a site. Finally, the Trimble malfunctions, fails to get reception, or runs out of power from time to time. This is extremely likely if you use your Trimble all day long in 100+-degree temperatures for 10–12 hours with the background map illuminated and all the other features on. Fortunately, you don’t the Trimble all the time if you have some paper maps or your map on a tablet, a pencil or stylus for the tablet, a ruler, and a compass because you can keep working in the project area and come back to record point locations when the GPS starts working again.
      3b) A PhD doesn’t need to know how to use a compass or a Trimble, but the best way to stay employed in CRM is to have an expertise in a certain area while also possessing a baseline competency in a lot of other areas. You need to be a general practitioner AND a specialist. Someone with a PhD is most likely going to be some sort of supervisor if they survive long enough. The best supervisors I’ve ever worked under had worked their way up from the bottom–starting as a field tech and working their way up to becoming a PI, department manager, or company owner. Being experienced with the various tasks expected of CRMers at every level is one of the things that made them good at their job. This means they knew how to use both a Trimble and a compass as well as a trowel, shovel, GSA rate schedule table, the full Microsoft Word suite, the written English language, basic algebra/geometry/statistics, ect… and were able to marshal their own personal skills, knowledge, and abilities to bring in contracts and manage co-workers. The reason why they’re the boss is because they know what they’re doing and have the personal skills to lead. In my experience, it is difficult to work with a supervisor who has not put in the work because they do not understand how the industry works.
      3 addendum) Many believe PhDs shouldn’t be expected to do field tech work. Many still believe PhDs are guaranteed to work in academia or in government administration. But, the Great Recession has rapidly fueled degree inflation in CRM. For years now, I’ve worked on crews where every single person out there had a MA or PhD and the PhD wasn’t always in charge of the project. We are entering a time when almost all field techs are going to have at least one Master’s or PhD. Companies have less incentive to hire BAs when they can build a SOI-qualified employee from a MA/MS/PhD. It is in the company’s best interest to hire techs with grad degrees as long as the employee can swallow their ego long enough to learn basic field archaeology and CRM. In this world of degree inflation and PhDs taking low wages just to work in their desired field, it is important for these MAs and PhDs to know basic field skills like how to use a compass and a Trimble. This is something I’ve been writing about on this blog for several years now.
      4) A bubble is necessary to balance a stadia rod or total station/theodolite tripod, but it’s not normal for an orienteering compass like the Silva Ranger. In my experience with the compasses i highlighted in the blog post, a small bubble tends to lead to a larger one. However, I was wrong in stating that any sort of bubble makes the compass inaccurate. The Silva website said your compass can get small bubbles based on elevation and a small bubble (less than 1/4 inch) will not impact the compass’ accuracy (https://www.silvacompass.com/frequently-asked-questions/#4). Hold off on tossing a compass that has a small bubble because it might go away if you change elevation. Thanks for bringing that up, Joe. I Sure wish I’d known that in the past.

      As always, I openly welcome criticism and commentary. This blog is supposed to be informative and we all learn more from lively discussion/debate than passively consuming content. Thanks for commenting. I appreciate it.

      Bill White