Author Topic: Numbering systems on the outside of a compass bezel  (Read 1717 times)

Rob Goes Walking

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Re: Numbering systems on the outside of a compass bezel
« Reply #30 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!
« Last Edit: 01:04:13, 26/04/19 by Rob Goes Walking »

Percy

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Re: Numbering systems on the outside of a compass bezel
« Reply #31 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

alan de enfield

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Re: Numbering systems on the outside of a compass bezel
« Reply #32 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 [size=78%] [/size]



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/



ninthace

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Re: Numbering systems on the outside of a compass bezel
« Reply #33 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 donít get me started on the joys of inertial navigation, which is not the art of map reading in bed.
Solvitur Ambulando

fernman

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Re: Numbering systems on the outside of a compass bezel
« Reply #34 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.

Rob Goes Walking

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Re: Numbering systems on the outside of a compass bezel
« Reply #35 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.