Compass?

Discussion in 'The Training Wing' started by Alina-Ann, Jan 30, 2008.

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  1. Heya, I have my MTQ1 exam coming up, and I'm hopeless at mapreading, so I want to buy a compass and have a bit of practise at home (I'm in the ULOTC). Does anyone know what the standard issued compass is? I have a feeling it's the Expedition Compass 4 (in Mils), but I don't want to make a mistake. Any help? Also, does anyone know where I can get hold of some random British military maps? I've asked at my unit but they never get round to it. Thanks. :)
     
  2. Quicksilva in mils graduation will do the trick. Tried asking the CQMS?
     
  3. ah ha, thank you! I thought it was Silva. As for asking the CQMS, he never seems to be about when I need him, but hopefully I'll just find a discarded couple of maps in the wreckage of the girls' locker room!
     
  4. Doh, I am getting confused. Yes Silva is the badger. Good luck on the MTQ.
     
  5. If your serious, a good mid range is here.
    Compass

    Any 1 to 50 thousand map of your chosen area should do.

    Try here for map reading made easy.

    Don’t forget to allow for deviation and variation. Mag to grid get rid, East is least West is best.


    Expect to get geographically embarrassed.

    Have fun
     
  6. Haha! I'm already geographically embarrassed because my section and I were doing night nav the other night, and we were rather hopeless. Thanks a lot for all your help!
     
  7. Alsacien

    Alsacien LE Moderator

    Pah!

    Don't waste your money on a new fangled compass.
    Get a sewing needle, a pair of ladies stockings, a bucket and some water.
    Not only can you have a compass, but by making a hole in the bottom of your water filled bucket you can also verify which hemisphere you are in :D
     
  8. if you are ULOTC the RSM runs the map store, speak to him nicely and he may get you a map to work with. Try one of your local area. Use it to practice nav round the area you are familiar with...

    Hope this helps.
     
  9. To teach yourself military map reading, you need:

    1. A Military map ('cos civvy ones aren't in mils)
    2. A Protractor 6", RA (in mils), complete with cord (the stuff that goes through the converging point of the radial lines).

    You don't need a compass. That's just for practicing navigation and even then, you only need it if visibility is bad. (If ever you really do need a compass (for quoting bearings), then you need a prismatic compass, but that's an advanced kettle of fish).

    METHOD

    1. Study the symbols and abbreviations at the bottom of the map. Memorise them. Find an example of each one on the map to help you visualise what they represent.

    2. Remember that the (supposedly) precise location of a feature is at the bottom centre of the symbol. It isn't always, it depends on the accuracy of the person doing the survey and of the person plotting the map, but this is how it's taught, so you must believe it to be true.

    3. Place the protractor on the map with the curved side to the right. Align the line that runs through 0 and 3200 mils on the protractor with any of the vertical grid lines on the map. The alignment must be absolutely precise! Look carefully at it for a minimum of 2 minutes. This is just to get you used to seeing how it is oriented correctly in relation to the map. You can put the protractor away for a while, the important bit has been done.

    4. Learn some terminology. The vertical lines on the map are called eastings. They tell you how far east something is. The horizontal lines are called northings. They tell you how far north something is. OK so far? There are no westings or southings. Look at the top edge of the map. There are numbers that increase as you look further towards the right. Look at the left edge of the map. There are numbers that increase as you look further towards the top. These numbers give value to the eastings and northings. The numbers are repeated in the body of the map so that you can use the map folded. Sometimes, one of the numbers in the body of the map is omitted. This is only because it would otherwise obscure a feature.

    5. Get a grid reference. At the bottom of the map is a box that describes how to allocate a grid reference to any point on the map. It will tell you that a full grid reference begins with two letters. You can forget this bit, the Army doesn't use them. Instead the Army uses the information in the box at the top right corner of the map - the bit with "Series" and stuff in it. To a soldier, the full grid reference is the information in the box, followed by the numbers that follow the two letters. I reiterate, don't use the two letters. Most initial training exercises will be conducted somewhere in the middle of a single map sheet, so you won't need to quote the Series etc. Major exercises usually put you on one map sheet and the objective on another. Map folds generally have a habit of occurring at important places, too.

    6. Accuracy of the grid reference. The grid reference used by soldiers is usually 4-figure or 6-figure. A four figure grid reference refers to an area that is 1km square. A six figure grid reference refers to an area that is 100m square. Note these are AREAS not POINTS. The area is positioned to the east and north of the point intersected by the first and second halves of the grid reference. If you want to give a grid reference to a feature smaller than 100m square, use a six figure grid reference and use the imaginary "tenth" lines to the left and below the feature. e.g. house at grid reference 549495. If you want to give a grid reference to a feature larger than 100m square, use a four figure grid reference. e.g. lake at grid reference 8494.

    7. Let's dispel some myths (1). Several units think they're dead clever and use 8 figure grid references, i.e. narrowing down an area to 10m square. Realistically, this is too small for most needs. Describing a target at this accuracy is, IMHO, OTT. If indirect fire weapons (e.g. artillery) are being used, there's a bloke who corrects the aim. As soon as he gives the first adjustment, the last figures of each half of the grid reference have gone out of the window. 6-figure grids are good enough and marginally quicker to use.

    8. Roamers. Get your protractor out again. Hold it the right way up. You'll find some L-shaped lines on it. These are called Roamers. Against each Roamer is a scale. Only use the Roamer that is the same scale as your map. In fact, get a fine permanent marker and draw a small circle centred on the junction of the axes of the 1:50000 Roamer. This will remind you that this is the one that you'll use most often, unless you're dead lucky and manage to get a 1:25000 map (typically range maps). Draw a small cross at the axis junction of all the other Roamers except the 1:25000 one. This will remind you that these are probably the wrong ones to use. Roamers are used to provide accurate grid references. To use the Roamer, place the junction of the axes on the feature you want to reference. Rotate the Roamer until one axis points left and the other points down, ensuring that these are exactly parallel to the grid lines on the map. Note where the axes cross the grid lines. Move the Roamer a smidgen left and down until the graduations on the axes are directly over the grid lines. The number of graduations between the grid lines and the junction of the axes provides the 3rd and 6th figures of a 6-figure grid reference. Don't forget that the easting forms the first half of the grid reference and the northing forms the 2nd half. If somebody gives you a 6 figure grid reference, place the junction of the axes somewhere within the grid square that 1st, 2nd, 4th and 5th digits indicate and adjust the roamer until the graduations correspond with the grid lines, ensuring that the axes junction doesn't stray out of the square. Good. Now put the protractor away.

    9. A mnemonic. You'll have heard the phrase "Across the corridor and up the stairs" or something similar to remind you to quote eastings first, then northings. Forget it. It's too easy to recite it the wrong way round. Remember what eastings are and remember what northings are. Then think about your favourite pastime - going out on the lash. You go out in the EVENING, overindulge and suffer the next MORNING. EVENING then MORNING. Say after me, "EVENING then MORNING." Now think EASTING then NORTHING. I've just made that up - it's a variation on what I've always used (In the 60s, the Warninks Advocaat advert had the phrase "Eveninks ant Morninks, I drink Vorninks" in a Dutch accent, of course. I just substituted Eastings and Northings).

    10. Map Bearings. Take out your protractor and place it on the map, aligned with the grid lines like you've been told. Pick a feature and put the axes junction of the protractor on it. Don't forget, if you're aiming at a symbol, you want to be at the bottom centre. You have kept the vertical axis of the protractor parallel to the eastings, haven't you?. Pick another feature, somewhere to the right of the protractor, and pull the cord that goes through the protractor so that it lines up with the new feature. Where the cord crosses the edge of the protractor, the bearing is shown by the outer scale. Remember, because the target feature is to the right of the initial feature, the bearing has to be between 0 and 3200 mils. Keep the protractor in the same place, but pick a feature that is to the left of the protractor. Now you'll have to rotate the protractor through 180 degrees (or 3200 mils), bringing the axes back to parallel with the grid lines. Pull the string as before and read off the bearing from the scale that reads from 3200 mils to 6400 mils. Doddle. Just remember, targets to the right have to be 0-3200 mils, targets to the left have to be 3200-6400 mils.

    11. Compass Bearings. You don't need a compass to learn this bit because it's easy. You point the arrow on the plastic part of the Silva (or Recta) at your target then rotate the bezel of the compass until the north markings within the housing align with the north end of the compass needle. Read off the angle. Told you it was easy - well, it is if you can keep the compass aligned with the target while you're doing this. The compass MUST be held horizontal!

    12. Magnetic variation. There are at least three Norths. There's True North. That's the direction to the point about which the Earth spins in the northern hemisphere. Think GLOBE and where the axle goes through the top. It's of no practical use to a soldier and few other people for that matter, particularly as the Earth wobbles, therefore it doesn't even exist. There's Grid North which represents the direction of the vertical lines on a map. These lines don't point to anywhere in particular, but all maps have them, so they're useful as a feature of uniformity. Then there's Magnetic North which is the direction that a compass points. At last, something that means something. Unfortunately, the Magnetic North Pole moves over time. At the bottom of the map, theres a diagram that relates these three Norths You can forget True North. The important bit is the value of the magnetic variation, i.e. the discrepancy between Grid North and True North. When you measure a bearing using a compass and want to plot that line on a map, you have to apply a correction. To do this, you subtract the magnetic variation from your compass reading and apply the corrected value to your protractor. You're going from a magnetic bearing (MAG) to a grid bearing (GRID) and subtracting (getting RID) the magnetic variation. MAG to GRID, get RID. It rhymes, so it's a good mnemonic. To take a bearing from a map to apply to a compass, you do the opposite. You add the magnetic variation. GRID to MAG, ADD. It almost rhymes, which is good enough. Don't forget that the magnetic variation varies with time. You have to calculate the number of years that have passed since the information was printed and multiply this by the annual variation, then add or subtract the resulting value from the stated variation, according to the printed instructions.


    11. Let's dispel some myths (2). You've got to learn about magnetic variation (and how to apply it) because it's part of the series of lessons. HOWEVER, if you're using a Silva compass you may as well not bother (but don't tell anyone that I said so). Silva compasses are meant for orienteering and it is assumed that an orienteer can read maps, so they're there to give the bloke a quick heads up about which way to set off. Even if they are manufactured to superb accuracy, the procedure of setting them throws in errors - just looking down at the compass and looking up at the target can inject an error of tens of mils, shivering and a sticky bezel can add more. So you end up with an error greater than the magnetic variation. Or, to apply logic, if Silva were worried about magnetic variation, they'd fit the compass with a slipping bearing scale (ask a mortarman or GPMG SF gunner) so you only had to worry about it once per map.

    12. Profiles(edit - See FFBox's 2nd post below). A fancy term that means draw a graph. Draw a line on the map (ALWAYS USE A PENCIL, NEVER PEN) from your start point to your objective. At each point where a contour line crosses your pencil line, as well as at the start point and end point, draw a perpendicular line of a length equal to the height of the contour. (You may have to subtract the height of the start point from each value if you're much above sea level). Join the tops of the lines and you'll have produced a graph indicating the hilliness of the route. Measure that line and you'll have a better estimate of the length of the journey.

    13. Common sense in the field (1). Don't pick a route where contour lines are close together. Experience (and the resection) will tell you what slopes are impractical.

    14. Common sense in the field (2). If you're marching along a compass bearing on a moonless night orin fog, don't aim directly at your objective. Aim off to one side. That way, when you reach a linear feature such as a road or tree line, you know which way to turn to bring you back on course. If you aim directly at your objective, unless you're extremely lucky and actually hit it, you could choose the wrong direction and massively increase the distance that you travel.

    15. Common sense in the field (3). If possible, avoid crossing open country in poor visibility. Follow a feature on the map - road, path, stream, pylons. These have changes in direction that are shown on the map and provide an aid to determining exactly where you are. The route may be a bit longer than the straight line drawn on the map, but the chances of you actually walking the straight line on the map are slim. At least you'll know how long it will take you to travel the intended longer route and you can programme your journey accordingly.


    Written down, it all seems a bit long-winded, but this lot can be demonstrated in about 15 minutes. After that, it's just practice.

    edited following FFBox's correction. Thanks, mate.
     
  10. Alina-Ann, check your PMs
     
  11. I've got the infantry basic map reading booklet on electronic copy if thats of any use.

    Its very good for teaching you the basics, which is what you need for MTQ1

    point 9, thats confused me no end, grown up on across the land up the stairs and never got it mixed up :D (yet)
     
  12. point 12 resection is the posh name for triagulation, using back bearings, you're thinking of intervisibility maybes?
     
  13. :oops: You're absolutely right. Point 12 should have been entitled "Profiles". In addition to the blurb I gave for it (difficulty and distance), it also provides the ability to determine areas of dead ground and hence whether or not you can see "the enemy" or they can see you. (For "enemy" you could equally substitute "Search and Rescue Teams" or "fellow walkers"), hence intervisibility.

    Resection is, indeed the method for determining your own position using two or more back bearings - two if you're near a ditinguishable feature, more to reduce errors if you're in the middle of a featureless landscape.

    Thus:

    16. Back Bearings (Resection). Take out your map and protractor. Mark a pencil cross anywhere near the middle of the left half of the map using a sharp pencil. This will be a nominal "You are Here" point. Using the principles of Point 10, determine the map bearings to two prominent features (mark these as Points A and B) that are generally to the right of the cross, but instead of just using the protractor cord, draw lines between the X and the chosen features. Ideally, the features should be selected so that an angle of about 45 degrees (800 mils) is formed between the two lines - this angle provides the best accuracy.

    Now move the protractor a scale distance of just 100m in any direction and (using the protractor cord) measure the map bearings to the same prominent features. You'll see that the bearings are different to at least one of the features. Clearly, only being at Point X will give the original bearings to both Points A and B.

    Now move the protractor to Point A and measure the map bearing back to point X. If you've done it correctly, this bearing should be 3200 mils greater than the bearing from X to A. (Don't worry if you're 10 mils or so in error but if the difference is more than 20 mils, re-measure both X to A and A to X). Now measure the bearing from B to X. Again you'll find that the difference between X to B and B to X is 3200 mils.

    It then follows that if you obtain a compass bearing (Point 11) to a prominent feature and convert it to a map bearing (MAG to GRID, get RID), you can add (or subtract, if the result would exceed 6400 mils) 3200 mils, place the protractor on the prominent feature and the bearing will line through to "You are Here" (an "A to X" line). This will tell you that you are somewhere along the line, but not where. You repeat the process with another prominent feature and obtain the "B to X" line. Where the two lines cross is your position.

    What's been done so far has just been to prove the principles, which is as far as self-learning indoors can cover. But, using the procedure in Point 12, just determine whether or not you would really have been able to see points A and B from Point X. No? Don't worry. When you go outside, if you can't see the prominent feature, you won't be able to pick them!
     
  14. msr

    msr LE

  15. Puttees, how about putting all that on Arrsepedia?, you know for all future ossifers!