Walking Forum

Main Boards => Gear => Topic started by: Rob Goes Walking on 16:39:01, 25/04/19

Title: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 16:39:01, 25/04/19
Oh dear I think I've made a mistake buying my compass. I expected the numbers to run 0 to 359 on the bezel but they don't, the run to 63.5 with the cardinals replacing some numbers. The compass I bought is a Silva Compass 4 Militaire on account of recognising the brand name, it being cheap for the brand, having all the map scales on it and saying it was luminous. What have I bought? Why is it numbered funny? Any suggestions on a replacement compass or how to use this one? While I suppose it would sort of work if all the bearings used the same system adjusting for magnetic declination would be tricky.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Mel on 16:47:17, 25/04/19
I just googled it.  The red and black numbers inside the twizzly bit look as if they're the numbers you need.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 16:49:36, 25/04/19
The clue is in the word militaire.  You have bought a military compass.  The army, god bless 'em use things called 'mils instead of degrees, makes it easier for the artillery to miss things. There are 6400 mils in a circle, if you want to know more, Google is your friend.  In the meantime, if you go into Kirkby Stephen tomorrow, there are, or were, two outdoors shops.  one near the market square on the left as you go towards Brough and the other on the left as you go the opposite way from the market square where you can get a proper compass. Best place to park by the way is the car park up towards the grammar school opposite the medical centre.  There is an alley from there past the cattle market to the square.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 16:58:16, 25/04/19
Thank you Mel and ninthace. The numbers inside the bezel are too hard to read off the index so close together, especially so close to the orienteering arrow for magnetic declination. I'll get another compass. Another lesson learned.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Pitboot on 17:00:07, 25/04/19
Using a compass with mils is just the same as using a compass with degrees, except the units are different.
North is still north and south is still south.
I learned to navigate at age 16 with degrees, joined the army, no difficulty using mils there, and as a civvy use degrees again, can't see the problem.
 It's sort of like using MPH and then having to think KPH when you drive overseas.
I still have a Silva compass from my army days marked in mils, it gets used a lot, and so does my newer degree marked compass. The only reason I sometimes use the newer one is that it has a 1:40000 scale on the base plate and I use Harvey maps.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 17:04:32, 25/04/19
Shops in Kirkby Stephen are Mad About Mountains and Eden Outdoors


Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 17:10:11, 25/04/19
Pitboot, part of the reason I bought this one is it has a 1:40000 scale on the baseplate (as well as 1:25000 and 1:50000). I could use it and use a calculator to get degrees in mils for magnetic declination. I'd rather have a civvy measuring system one though I'm not the military!

Thanks for the shop info ninthace.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 17:23:09, 25/04/19
Small military joke.  There are two Corps in the Army with the same motto - Ubique.  The Royal Engineers and the Royal Artillery (see this creeping back to a mils reference?).  For the Royal Engineers Ubique means "Everywhere" to signify that they have been present at all the Army's major battles.  For the Royal Artillery it also means "Everywhere" or perhaps more precisely "All Over the Place".
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 17:27:53, 25/04/19
Very good. On the subject of jokes and engineers:

A man is flying in a hot air balloon and realizes he is lost. He spots a man down below and lowers the balloon to shout: “Excuse me, can you help me? I promised my friend I would meet him half an hour ago, but I don’t know where I am.”

The man below says: “Yes. You are in a hot air balloon, hovering approximately 30 feet above this field. You are between 40 and 42 degrees N. latitude, and between 58 and 60 degrees W. longitude.”

“You must be an engineer” says the balloonist.

“I am” replies the man. “How did you know.”

“Well” says the balloonist, “everything you have told me is technically correct, but I have no idea what to make of your information, and the fact is I am still lost.”

The man below says “You must be a manager.”

“I am” replies the balloonist, “but how did you know?”

“Well”, says the man, “you don’t know where you are, or where you are going. You have made a promise which you have no idea how to keep, and you expect me to solve your problems. The fact is you are in the exact same position you were in before we met, but now it is somehow my fault.”
Title: Re: Numbering systems on the outside of a compass bezel
Post by: alan de enfield on 17:37:40, 25/04/19
Many years ago I was teaching orienteering at an International Scout camp.

I had one team which seemed to have a consistent problem in heading off at the correct heading, called them back, off they went again in the wrong direction, called them back ………….. same again.

They were a group from Norway, and on closer examination their compass was a 'metric' compass that has 400 degrees and a right angle (ie due East) was 100 degrees.

I subsequently found out that in fact it was a 'Gradian' compass with 400 grads to a circle / 100 to a right angle.

As an aside...  NATO military compasses use 'mils' which range from 0-6400. The 'Mils' system is based on Radians. There are 2π Radians in a circle. So technically there are 6283 mils in a circle, but this gets modified to 6400 for convenience except for the Swedish armed forces which round it to a more exact, but slightly more annoying 6300 and former Warsaw Pact countries which round down to an anticlockwise 6000 mils - so beware of buying old Soviet-era compasses.

Surveyors and other militaries may use gradians. They are the metric form of Degrees - there are 400 Gradians in a circle.

The mils system has the useful property that 1 mil subtends 1 meter at 1 kilometer. Useful when calling in direct (machine guns) or indirect (mortar, artillery) fire.

Hey, some fellow hikers can be annoying. You just never know when this information can be useful… For civilian uses, degrees are the norm.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 17:50:33, 25/04/19
Interesting and educational post Alan,  ;D at calling in fire on other hikers. Apart from the ones who hog the summit when others are around (I think they're known as summit slugs around this forum) I've yet to be annoyed be another hiker. I'll give it time.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Pitboot on 20:05:46, 25/04/19
My experience of the "dropshorts" when training in Canada was that despite sending them an eight figure grid reference and accurate adjustments in 100 mil increments they still managed to lob their 105mm bullets somewhere between me and my HQ troop.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: archaeoroutes on 21:22:50, 25/04/19
There is actually no need for the numbers in most navigation. You set the compass from the map and then walk on it - no need for numbers.
Of course, when there's a significant variation, there'll be a need to correct for it, but even then only the divisions matter, not the actual numerical bearing.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 21:32:12, 25/04/19
There is actually no need for the numbers in most navigation. You set the compass from the map and then walk on it - no need for numbers.

Good to know. The only ones in the book which the numbers mattered for (apart from adjusting for magnetic declination) I think were running bearings and double bearing in the advanced section and only then as limits you could calculate in mils. I do realise I'm being a bit precious sending my Militaire back and getting one in degrees but I'll enjoy it more if I'm pleased with the kit.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Mel on 22:03:11, 25/04/19
.... No need to worry about magnetic declination either in this country.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 22:08:37, 25/04/19
.... No need to worry about magnetic declination either in this country.

It did look like a small error but I wasn't sure how much error it would bring in practice. I think I can calculate using mils! So (6400 / 360) * 2 = ~35.5 metres error every kilometre, is that right? Or does it change depending on the angle?

Edit: No I'm fairly sure it shouldn't change with the angle.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: archaeoroutes on 22:28:14, 25/04/19
Bear in mind that its not possible to set a compass better than a couple of degrees anyway (just like you can't read a millimetre ruler to better than 1mm). Then remember that following a bearing to degree accuracy is really unlikely to happen. So a degree or so variation isn't going to be significant.


I get what you mean about needing to be happy with your kit.
I've got five different compasses, each with their own pros and cons. I use them all at various times as each has a situation where they excel.
I have also been through many iterations of some kinds of kit because they just weren't perfect.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: sussamb on 22:37:56, 25/04/19
My experience of the "dropshorts" when training in Canada was that despite sending them an eight figure grid reference and accurate adjustments in 100 mil increments they still managed to lob their 105mm bullets somewhere between me and my HQ troop.

Even worse when they're US troops, nearly killed twice by US fire supposedly in support  ;D
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Innominate Man on 22:44:11, 25/04/19
Not the best tutorials but 'certainly worth knowing' are the series made by Lyle Brotherton. He could be the author of the manual you bought.
https://www.youtube.com/watch?v=BADUq3Maqbo (https://www.youtube.com/watch?v=wPP8F7nexGk)
Also, and perhaps better are similar tutorial youtube vids by Glenmore lodge.
All of these tend to give you that familiarity that you'd gain from being shown by somebody rather than simply reading a manual.
Check them out, if nothing else they may confirm that your understanding of the manual is correct.


Watch out for Lyle's cat  ;D
Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 23:02:27, 25/04/19
Even worse when they're US troops, nearly killed twice by US fire supposedly in support  ;D
Watch out for RAF Regt (Rockapes) too.  A Rockape boss of mine told me a tale that happened when he was in a sandy place long before the recent unpleasantnesses - Oman I think.  As a Junior Officer he was forward, conducting a mortar shoot.  He gave the fire order and asked for "one for effect".  There was muffled crump from somewhere but no sign of the explosion so he ordered "up 100" or whatever it is pongos say.  At this point his NCO drew his attention to a newly formed hole in the desert about 100m behind them and suggested he didn't ask for another. one, or words to that effect.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Mel on 23:07:49, 25/04/19

It did look like a small error but I wasn't sure how much error it would bring in practice. I think I can calculate using mils! So (6400 / 360) * 2 = ~35.5 metres error every kilometre, is that right? Or does it change depending on the angle? Edit: No I'm fairly sure it shouldn't change with the angle.



I've no idea what you're on about. 


I've never adjusted my compass readings for magnetic variation.  It's only about 2 degrees in this country anyway and for the (relatively) short distances of travel before changing direction, I wouldn't say it's that important.


Walking on a bearing just means you've pointed your compass in the direction you want to travel, twiddled the compass housing so the arrow shape is pointing in the same direction as the red bit of the compass needle and whatever the number says (be that in mils, degrees, or whatever) is your "bearing".  But in reality, all you're doing when walking on a bearing is making sure you keep the red needle in that arrow shaped bit whilst walking in your "direction of travel arrow" direction.  The numbers are irrelevant.


The only time a bearing (number) might be relevant is if written walk instructions say something like "from point A walk for 400 metres on a bearing of 270 degrees to point B" (or mils, or whatever).  In reality, all that means is you turn your compass housing twizzly bit to 270 degrees, line your arrows up by (this time) turning the whole compass (not the twizzly housing bit) and off you go along your direction of travel arrow.


If I was to walk in a straight line from my house to the church, I would be walking on a bearing of 260 degrees.  For the short distance that would be (half a mile) making any magnetic variation adjustments would make no difference at all to where I would end up. It's not unreasonable to walk that sort of short distance before needing to change direction (and, thus, your bearing).



I can't believe I just dug my map and compass out to do that  ;D 

Title: Re: Numbering systems on the outside of a compass bezel
Post by: pdstsp on 23:15:38, 25/04/19
Mel's answer above just about covers it, in my experience.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Mel on 23:27:01, 25/04/19
My cat is asleep 6 feet away from me on a bearing of 291 degrees.
 
My kettle is 10 feet away from me on a bearing of 160 degrees but to get to it I actually need to walk 2 paces at 249 degrees, 3 paces at 149 degrees, then 2 paces at 72 degrees.
 
Oh god.  Look what you’ve set me off doing.  Indoors nav practice  :-[
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 23:34:04, 25/04/19
Yes IM he is the author. His descriptions were very clear I did understand them when I read them though not all the methods of procedure stuck, that will require practice.

I know know of enough techniques to be able to navigate around with a good idea of my current position, various ways to confirm my position and ways to relocate myself, using only 1 feature if necessary. What I don't yet know is how good I'll be at doing it but practice makes perfect (or hopefully good enough in this case). Route stories was the only thing from outside the book I required to make sense of it.

I'll save the videos until after I've practiced the techniques which will take several days if I follow Lyle's advice. Don't want to overload myself with information. I'll watch them before setting out on a real route instead of playing in the park.

Plus I want to know if I can learn navigation just from this book, route stories notwithstanding.

Or maybe curiosity will get the better of me and I'll watch them sooner. Probably.

Thanks for the links.

Mel it's how many metres west you will drift every kilometre you walk if you don't adjust for magnetic declination although as pointed out, it won't be quite that precise as the adjustment won't be 100% correct. As an average though it should be roughly correct. Dr Ninthace, was my sum correct? Seeing as you don't walk in perfectly straight lines (drift) and may not 100% accurately know your position (for resection) I'm sure this error is trivial but I'm still going to correct for it, trivial or not.

 ;D at indoor nav. I was practicing keeping my map orientated indoors earlier!
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Mel on 23:46:57, 25/04/19
The westerly drift difference would be about a couple of metres (two stride lengths, or thereabouts) over a kilometre.  Big wow.  By all means spend time learning it but, in practice, it's simply not needed in this country (IMO). 


Anyway, I'm navigating myself to bed .... on a bearing of 200 degrees and 20 foot of ascent  ;D






Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 23:49:21, 25/04/19
The westerly drift difference would be about a couple of metres (two stride lengths, or thereabouts) over a kilometre.  Big wow.  By all means spend time learning it but, in practice, it's simply not needed in this country (IMO). 


Anyway, I'm navigating myself to bed .... on a bearing of 200 degrees and 20 foot of ascent  ;D

So you're saying over 1 kilometre, 1 degree causes 1 metre of drift, not 1 mil as Alan said? Maybe Alan meant something to do with the vertical properties of the artillery fire not metres of horizontal distance like I took it - I can't remember exactly what he said nor did I understand it completely when I looked up the word he used in a dictionary. I could always plot 2 degrees on my map and measure the distance over 1km I suppose.

I want to learn to do it properly even if it's not needed.

Good night! Sleep well.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Innominate Man on 23:56:38, 25/04/19
Not entirely relevant to this debate but related and interesting (well, to me anyhow) is how some aspects of measurement & positioning are very precise.
Many years ago, as part of my vocation training I had need to understand surveying techniques, which I found really interesting and totally practical:- you knew if you were right because certain things were proven.
Anyhow, what I am getting to is that within a short while after the basics you learn how to make certain corrections within your calculations and one of these is an allowance for the curvature of the earth.
You may think that on a local level it isn't discernible, but I can assure you it is.
I know of an instance where a major survey at an airport for a runway extension had been undertaken and they were having all sorts of problems with the results. A friend of mine, of the old school, was sent to troubleshoot.
Despite protestations to the contrary 'that of course they had allowed a curvature correction' the autopsy proved otherwise !  My friend was vindicated as it was his first hunch that the amount of error indicated no such allowance had been included.
By the way, the learning of this was the manual way and didn't include any GPS technology (mainly because it didn't exist at the time !!)
So whether it is a building, a football pitch an airfield or the Everest range - it is 'certainly something worth knowing'.


But, despite professional accuracy - I agree with Mel, keep it simple. You don't need to know how to perform a lobotomy to cure a headache  ;D    

Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 00:19:33, 26/04/19
IM, I've been accused of being excessively precise before. I just like knowing the numbers...
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 00:31:22, 26/04/19
According to this page:

https://whitehatcrew.com/blog/a-mere-one-degree-difference/

My math wasn't far out. It's close to 35 metres of westerly drift, the half metre error comes from rounding in the mils system, there are 6283 mil-radians in a circle not 6400.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 00:44:17, 26/04/19
Mel it's how many metres west you will drift every kilometre you walk if you don't adjust for magnetic declination although as pointed out, it won't be quite that precise as the adjustment won't be 100% correct. As an average though it should be roughly correct. Dr Ninthace, was my sum correct? Seeing as you don't walk in perfectly straight lines (drift) and may not 100% accurately know your position (for resection) I'm sure this error is trivial but I'm still going to correct for it, trivial or not.
It has been a while so I am open to correction by one of the cognoscenti but IIRC if you walk 1km on a magnetic bearing your drift from the true bearing is the sine of the declination times the distance gone. Say the declination is 2 degrees and the distance gone is 1km. Sin(02) is 0.0349 so the distance off track will be 1000x0.0349= 34.9m. We never had declination when I was alive, we had variation and deviation.
However, it will be a clever person that can walk 1km in a straight line across the countryside armed only with a compass and arrive within 35m of where they are supposed to be so to all intents, you can ignore variation in the UK given its current low value. Mind too, I could get pretty close with a Garmin.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 00:51:25, 26/04/19
Your maths and mine make it exactly the same if you look at the post just above yours ninthace so I think it's right.

Yes I could ignore it as you all say but I still like to know the numbers. 8)

(There isn't a nerdy looking forum face so I've got cool shades on instead).

I didn't know Sin was used like that. Wondered what it did. I just had a quick Google to read about it but as with so many things like that, the more I read the more there was I didn't understand and the more I had to learn until I lost interest as there were too many new technical terms to learn just to get the gist of Sin and the gist was all I wanted, not a complete lesson on trigonometry. I guess though ninthace you have already given me the (very rough) gist of it!
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Percy on 07:53:31, 26/04/19
As ninthace posted a simple bit of trigonometry gets you the answer. As a rule of thumb there is the 1 in 60 rule:


https://en.m.wikipedia.org/wiki/1_in_60_rule (https://en.m.wikipedia.org/wiki/1_in_60_rule)
Title: Re: Numbering systems on the outside of a compass bezel
Post by: alan de enfield on 08:07:29, 26/04/19
Not entirely relevant to this debate but related and interesting (well, to me anyhow) is how some aspects of measurement & positioning are very precise.
 ;D  



Very true.
Totally of topic (well - maybe tangential).


When shooting over long distances (1000 metres) you have to take into account the coriolis effect, this is where the rotation of the earth affects an object in free space.


Whilst the bullet is in the gun, held by the person, standing on the Earth the bullet is moving in the same direction and at the same speed as the Earth.
Once the bullet is fired and is 'in the air' the Earth continues rotating whilst the bullet goes into a straight line towards where the target WAS when the bullet was fired.
By the time the bullet arrives at the position the target WAS at it has moved many inches to one side.


https://loadoutroom.com/thearmsguide/external-ballistics-the-coriolis-effect-6-theory-section/


Title: Re: Numbering systems on the outside of a compass bezel
Post by: ninthace on 08:27:20, 26/04/19
Which explains why so many folk wonder round in circles. The secret is only to walk east or west folks!  :)
Now don’t get me started on the joys of inertial navigation, which is not the art of map reading in bed.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: fernman on 09:13:57, 26/04/19
it will be a clever person that can walk 1km in a straight line across the countryside armed only with a compass and arrive within 35m of where they are supposed to be

I couldn't agree more. In undulating upland country with rises, dry valleys, rock outcrops, boggy areas, large beds of rushes, etc., it is absolutely impossible to walk in a straight line following a compass bearing.
Title: Re: Numbering systems on the outside of a compass bezel
Post by: Rob Goes Walking on 09:31:18, 26/04/19
As ninthace posted a simple bit of trigonometry gets you the answer.

It's only a simple bit of trigonometry you know trigonometry! I just looked up the meaning of the word:

Trigonometry (from Greek trigōnon, "triangle" and metron, "measure") is a branch of mathematics that studies relationships between side lengths and angles of triangles.

So had I known what trigonometry was (other than the bit of maths dealing with Sine, Cosine and Tangent, mysterious functions I've copied and pasted - my understanding of trigonometry) I still wouldn't have known I needed trigonometry without knowing it.

It's only easy once you know! My corrected sum based on Alan's lesson about mils is also simple ((6283 /360) * 2) and was only 6 millimetres out. Don't think I did too badly with my limited knowledge of maths.

Crikey I learn a lot more than just walking here.

I get that there will be other errors introduced by walking as you all point out but if I've broken the nav rule of my book and don't have an attack point within 500 metres, all the more reason to do it properly and correct for it - it's an additional error I can do without. Will it matter in practice? I'll take the forum at it's word it won't.