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Saturday, August 5, 2017

Buying a Compass

The first thing you need to land nav in any useful way is a magnetic compass. Simply being able to orient yourself to where north is, or keep yourself on track no matter the terrain and lighting gets you way ahead of the game.

Squad leaders are briefed, with a map and protractor out during the brief. Consistent, well-communicated position information is critical to operational planning and actions.

Compatibility

The first thing to consider is that you likely work with others. You all want to be speaking the same language, and to be able to brief in things like declination changes to everyone at the same time.

Speaking the same language is basically one of mils vs degrees. A circle can be broken up any number of ways, and a number of them are not useful for our purposes so we shall not speak of them. Degrees are very common, well-understood, but not used by most military forces.

Instead, they use mils, which is just short for milliradian. That's an SI-derived unit of angular measure which is a thousandth of a radian. A radian is the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle. Yeah, don't worry about that, as you don't need to know. There are about 6283 milliradians in a circle, but again, you don't need to know that, exactly.

Because it's an inconvenient number. Instead, armies have standardized on various other rounded off versions. The WARPAC generally agreed to call it 6000, the Swedish Army (they make the best compasses, so we care) had 6300, someone had 6280, and many others. This does matter because NATO settled on a nice easily-divisible 6400 a while back, so many good military surplus "mil" compasses are surplus because they are some other weird, antiquated number.

That matters for compatibility. If you are in a team and they say to march at a certain heading until you reach a road, your 6000 mil compass is pointing a different direction than their 6400 mil one.

Ask Someone

If you work with a team of people who probably carry compasses, start with asking them what they suggest. Then, read carefully, and check my last section. Because if they say "you can get it at WalMart" then be really, really careful.

Types of Compasses

There are lots and lots and lots of types of compasses. But there are really only about 2-1/2 kinds that are in common use these days for land navigation in the west. 

Baseplate

Clearly, most compasses can be considered a capsule attached to a baseplate but here we mean a particular style of compass which is:
  • A base with marks for alignment and plotting. You want a clear base with scales included for typical maps
  • A rotating, liquid-dampened capsule
This is a very general category. There are many, many sub-variants with additional features. The basic baseplate we're talking about has no additional sighting features, so practically is only capable of moderate precision, or takes additional skill by the user.

Benefits

  • Huge selection of styles, sizes and features
  • Light weight, compact
  • Extremely simple to use. Almost anyone can figure out the basic operation with little or no instruction
  • Low cost; even expensive models are only relatively expensive
  • All in one. The baseplate includes the features of a roamer or "protractor" with scales and plotting aids

Gotchas

  • There are almost no good night capable baseplate compasses. There are a number with tritium, but not very robustly employed so they are hard to fully use. Most do have plenty of phosphorescent bits, so you can use a tiny UV light to make them glow enough to navigate at night. 
  • They are plastic so can be broken under extreme conditions; I've seen them break
  • Not all features are implemented the same way, so it can be hard to train a group who all have different baseplate compass models
  • Most have only degrees or mils, not both; the few with both usually have one prioritized; in the photo above, it is hard to get accurate readings off the degree scale, for example
  • Many surplus compasses with mils are not 6400 so are hard to use properly in a team environment or with conventional training materials

Notes about Fluid Damped Compasses

Dampening is critical. Without it, the needle would wobble back and forth around the direction it wants to point and you would have to set the compass down and come back a few minutes later. 
  • Most are regional compasses. The shallow capsule requires the needle to be balanced for certain parts of the world, and going somewhere else can make it drag and read wrong
  • Some may get bubbles from large elevation changes. Bubbles can interfere with accurate readings, but generally go away if it is left alone at the use altitude for a few days or weeks

Mirror

The mirror or Ranger compass is basically a Baseplate compass with a mirror. The mirror generally acts as a cover for the compass, but when erected is used to give a sighting line and reflect the capsule position for use in sighting and measuring angles with much more precision.
Yeah, most people think the mirror is for putting on your makeup or signaling airplanes but that's not what it is for. The mirror is a key part of making the compass work better. The top is brought up so you can use the mirror to see the capsule.
You then use the sight notch and the line on the mirror (not all have the line) to sight precisely to the target, while you keep the capsule in view to make sure it is level and so on. When reading a locked in bearing, to find a point to walk to or so on, you can turn your body slowly to move the compass until the needle lines up with the capsule marks, then see what is over the sight notch. So, helpful both ways.

Benefits

  • Same as baseplate and can be used like a baseplate, but also... 
  • Higher precision
  • Protected capsule, so overall stronger and less prone to damage when stowed

Gotchas

  • Same as baseplate but generally not as fragile
  • No better on night use that I've seen
  • No freebies for precision; it takes time to take those better sightings

Lensatic

By this we only mean the post-war USGI issue compass and commercial versions of it. It is a folding, metal bodied compass with a magnetically dampened, globally-capable capsule.


There is a simple scale along one side, the lid can fold up halfway as a sighting system not unlike the mirror compass, and there's a lens (lensatic!) that allows you to place the compass close to your eye, and both sight into the distance, and glance down to read the numbers on the capsule.

Benefits

  • Standard. Everyone who' been in the military should know how to use one, though practically it's not taught a lot anymore
  • Very sturdy
  • Fits into compass pouches
  • Tritium models are by far the best night-usable compasses

Gotchas

  • Heavy, bulky, pokey. Needs to be in a compass pouch as it's not going in a top pocket or anything else
  • Requires additional materials (a roamer or "protractor") for plotting on maps; the way the compass operates simply does not account for this without orienting the map, and there are no scales on the base
  • Issued for a long time so many are very old; be careful buying used
  • Lowest bidder, so quality is hit and miss. Some broken, flawed in various ways which is bad for a precision instrument
  • Scale on the side of the compass is very coarse so hard to use
  • Features are complex so requires training to understand and use properly


Knockoffs, Mergers, and Lies

We nailed the technology of compasses long ago, so there is infinite selection of them. First, avoid anything with no name, or a name you haven't heard of.

Funny Foreign Military Issue Compasses

Many of you may have a funny foreign compass, or run across one at a surplus store. They may be nice, but often these are like the USGI compass in that they have neat features which... we won't know about. Collect them, but I'd avoid using one.

Big Names and Mergers

Then there's the big names, and even there things are a bit troubled. The big names (at least in baseplates and mirror compasses) have been Silva, Brunton and, Suunto. Now I've lost track of all the intrigue, but various weird corporate mergers and stuff means that there are no Silvas imported into the US.

Oh, you say you can find some? They are Brunton-made (east-Asia low cost imported, mostly) compasses, with the Silva name.

Often, they are Brunton-designed and purchased, sold in the US market, but only have the Silva name and model number. They are often made in cheap overseas factories, or modified from the original design. Sometimes horribly so. Some of my favorite Ranger compasses are no longer available officially as the Brunton-ized version has a plastic hinge.

I don't mean plastic cased with a pin like a hinge is on a door. I mean the top and bottom cases are one piece, then they just fold it. Fold too many times, it breaks into two pieces.

Brunton even sells compasses they do not build and maybe didn't design. There's one branded by them that appears to be a nice version of the USGI lensatic. It indeed only appears that way. Cheap, liquid dampened, and so poorly made it is often several degrees off. Be careful what you buy.

So, while those three brand names are still about the only good ones, be careful what you buy from them. In general, I wouldn't buy from WalMart or Target, but go to a serious camping store. Even then, I'd keep in mind all the risks and bad stories shared here, and look closely at it. If you buy online, make sure you can return for free if its not what was advertised. Yes, Amazon was selling photos of real-hinged Silva Rangers and the reviews warned they were actually plastic hinged US made knockoffs with many other issues.

There are a few other brands which are either old so you are buying used, or are not much or officially imported to the US. K&R seems to be a very good maker, but has few mil compasses and I've never seen one. Recta made Swiss and French military issue compasses, but got bought by someone so doesn't really exist anymore. And so on. Ask if you have a known brand and want to find out our thoughts. 

Tritium vs Phosphorescent

Lastly, let's talk about night use, and tritium in the USGI compasses. At night, your compass must glow. It can do that one of two ways:


  1. Phosphorescent – Or "glow in the dark" paints, inks and dyes are applied to the numbers, needles or backing of them. They absorb UV radiation and covert it to visible light, but transition between these states very slowly. 
    • Note they use UV light, not white light. LEDs are very narrowly focused so have no spare frequencies they emit, so you will need a UV keychain light to "charge" your phosphorescent compass, cateyes, etc.
    • Someone at Cammenga, the maker of the USGI compass for some years is a bit stupid, and no one else cares so they have for decades clearly labeled their phosphorescent compasses "Phosphorus." 
    • Radioluminescent – A radioactive source emits radiation during decay which is converted by materials much like those in phosophorescent systems to emit visible light.
      • Radium clock dials did this in a very convenient way, painted on only, but long before anyone cared about not killing their workers in truly horrible ways, so those are long banned. 
      • Today we use tritium, which is a radioactive gas, in tiny tubes. The inside walls are coated in powders that emit visible light. 
      • Tritium has a half life of (about) 10 years. Not a life, a half life. Half the tritium decays every ten years. So the tritium vial is half as bright after 10 years, half again as bright after another 10, etc. It never dies, just gets very dim. 
      • Tritium sources are VERY BRIGHT for a compass when new. 10-15 year old ones are a nice brightness, and will last you about 10 years before they get anything like too dim. 
      • Date codes for Cammenga compasses (most other USGI makers are probably too old now) are stamped on the inside of the lid of the compass. It's three numbers, but un-obviously: Year, Month, Lot. So "09 04 71" is made April 2009 and you ignore the last two digits. They are a bit unclear, but we tend to assume they use fresh tritium vials. 
      • Tritium is not at all dangerous. It is a tiny, tiny, tiny amount of a not particularly poisonous or radioactive material. Someone I know who works with this stuff had the math done: you would have to break 10,000 of them, at once, in a sealed phone booth and breath deeply to maybe, possibly become sick from it. 
      • Many, many, many seller of USGI compasses claim they are all Tritium. They are not. Be sure it is before you pay Tritium prices. 
      • It is hard to get the very good tritium illuminated European compasses as importation of even minorly radioactive stuff is full of paperwork. Most don't bother, so official, new models of these simply do not exist for us. Some pop up on eBay, or you can fly to Europe. 

    So where Do I Buy From? 

    Just knowing what to watch out for makes you a smart shopper and you can probably safely buy from anywhere, or walk away when you see nothing good. But good stores are nice because they rarely have garbage and you can trust anything.

    There aren't a lot of these. REI, EMS, MEC, CampMor and the like are not bad, but are mass market enough (selling workout clothes and so on) they sometimes have crappy compasses alongside the good ones.

    The only one I really know to be good now is Ben Meadows. They are a supplier of products for forestry and professional outdoorsy types, and have a wide range of prices, though most or all are in degrees if that matters to you.

    While I have never bought from them, Forestry Tools has some of the rare, cool and very expensive Silva Expedition compasses. Note the "6400" in the name should make you excited if you actually read this whole article.

    I buy a lot from the usual places I buy everything, Amazon and eBay. Surplus stores can also be good, but are the same for compasses as everything: un-knowledgable, often sell knockoffs, and sometimes overpriced. But sometimes you can find a deal because they don't, for example, get the difference between tritium and not or because they think a Rothco knockoff the USGI is worth more than any plastic frenchy compass so you can get something odd but awesome for a steal.

    Now, Learn How To Use It

    A tool like a compass is no good without training, and practical experience using it. CWG can get you that. Start planning for CWG's day/night land nav training course in October.

    Sign up now





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