LESSON 12 MAP READING ROMERS AND PROTRACTORS Reference: Aids: Manual of Map Reading and Land Navigation 1. Slides 12/1 to 12/13. Place of Work: 2. Lightweight Compass per student. Classroom and Outside Area 3. RA protractor per student. Student Dress: 4. 1:50,000 map sheet per student. Working Dress 5. Pencil, paper and ruler per student. Equipment: Administration: Projector and Screen 5. Read the Instructors Notes before the lesson. 2. Check RA Protractors New/Old. 3. ........................................................... 4. ........................................................... Time Allowed: 40 Minutes 12-1 BEGINNING OF LESSON STAGE Revision CONTENT Write down the grid references of the four places of worship shown on the slide. SLIDE 12/1 ANSWER: Discuss the answers particularly those answers that disagree by 100 metres in Eastings and/or Northings, but leave the final result of the discussion “hanging”. Aim The aim of this lesson is to teach you how to use a Romer and the RA protractor. Objectives By the end of this lesson students will be able to use: 1. The Romer on a Lightweight Compass to obtain more precise grid references. 2. The Romer on an RA protractor to obtain more precise grid references. 3. The RA protractor to plot and measure bearings. Reason Why When giving a grid reference or bearing it is sometimes essential that there is no doubt over the feature identified. Incentive Identifying the correct feature by grid reference or bearing means that RVs are kept, resupply goes to the right place, and attacks take place where they should. 12-2 MIDDLE OF LESSON INTRODUCTION In an earlier lesson you learnt to estimate grid references to an accuracy of a hundred metres. Your grid reference could have been up to one hundred metres North, South, East or West of the true position. Today you will learn to use a ROMER so that you will obtain the SAME grid reference every time. THE LIGHTWEIGHT COMPASS ROMER What is a Romer? A Romer is a device which you can use to accurately divide a grid square into 10 equal parts in Eastings and Northings. How is a Romer used? Pick up your Lightweight Compass. SLIDE 12/2 You already know how to use the Lightweight Compass for bearings. Near the direction of travel arrow are three scales, called Romers. The scales of each Romer are marked on the compass. At the moment you are only going to use the 1:50,000 scale Romer. TO TAKE A GRID REFERENCE USING A ROMER DEMONSTRATE how to take a grid reference from a map using a Romer. SLIDE 12/3 1. Place the Lightweight Compass on the map with the corner of the Romer on the feature. Make sure the two edges of the Romer are parallel to the grid lines. EASTINGS 2. Read the Eastings grid line for the first two figures of the grid reference and, on the Romer, count whole divisions left from the point to the Easting grid line to obtain the third figure. NORTHINGS 3. Read the Northings grid line for the first two figures of the grid reference and, on the Romer, count whole divisions down from the point to the Northings grid line to obtain the third figure. 100 Metre Square The grid reference actually identifies the bottom left-hand, or SouthWest corner, of a one hundred metre square containing the feature. Here are more examples using the Lightweight Compass Romer. SLIDE 12/4 Note: Do not forget the 100 kilometre letters for a full grid Any Questions Questions from the class. Confirmation Practise the class in taking grid references using the Lightweight Compass. See Instructors Notes TO PLOT A GRID REFERENCE USING THE DEMONSTRATE how to plot a grid reference on a map using a Romer. 12-3 ROMER SLIDE 12/5 1. Look for the Eastings and Northings grid lines to identify the one kilometre square. 2. Place the Romer in the square. EASTINGS 3. Set the Romer against the left Eastings line by using the third figure of the Eastings. NORTHINGS 4. Set the Romer against the bottom Northings line by using the third figure of the Northings. This grid reference identifies the bottom left-hand, South-West corner of the 100 metre square, which contains the feature. Here are more examples of using the Romer to plot grid references: SLIDE 12/6 Any Questions Questions from the class. Confirmation Practise the class in plotting grid references using the Lightweight Compass. See Instructors Notes INTRODUCTION TO THE RA PROTRACTOR The RA protractor is the standard issue protractor. It is used for plotting and measuring bearings, measuring distances, and for giving accurate grid reference by means of the Romers. RA PROTRACTOR ROMERS Pick up your protractor and find the 1:50,000 Romer. SLIDE 12/7 Note: There are TWO 1:50,000 Romers. There are METRE Romers on the LEFT-HAND side of the protractor and there are YARD Romers on the RIGHT-HAND side. DO NOT USE YARD ROMERS, repeat - DO NOT USE YARD ROMERS. Put tape over the yard Romers. SLIDE 12/8 The 1:50,000 metre Romer on the RA protractor is used in exactly the same way as the Lightweight Compass Romer. Note: There is a handy little hole that can be used to mark a grid reference. Any Questions Questions from the class. Confirmation Practise the class in plotting grid references using the RA protractor. See Instructors Notes USING THE RA PROTRACTOR The main use of the RA protractor is to measure and plot Grid Bearings: Pick up your RA protractor. SLIDE 12/9 The RA protractor is similar to the protractors that you used at school, except that it is marked in mils and works from the North-South Grid Lines. 12-4 Each division is 10 mils with a bolder division every 50 mils. The 10 mil division run from 0 mils to 3200 mils and there is an inner set of 10 mil divisions marked from 3200 mils to 0 mils (6400 mils). Note: There is a numbered value every 200 mils and there is an additional 150 mils at each end. (To save turning the protector around) When you use the RA protractor you always put the CENTRE POINT over the feature. DEMONSTRATE placing the protractor over a feature. MEASURING GRID BEARINGS To measure a Grid Bearing on a map. 0(6400)-3200 MILS 1. Draw a line on the map between the two features. Make sure the line is at least eight centimetres long so that it is not hidden under the protractor. 2. With the straight edge of the protractor to the left, place the centre point at one end of the line, making the scale or Romer lines parallel to the North-South grid lines. 3. Read the bearing in mils where the pencil line touches the protractor. See Instructors Notes SLIDE 12/10 Note: You are using the OUTER SCALE because the bearing is between 0 to 3200 mils. Remember that Grid Bearings are measured clockwise from Grid North. Note: It is not possible to obtain an accuracy greater than 10 mils. Practise Give the class two grid references and ask them to find the Grid Bearing from one to the other. Ensure that the bearing is between 0 and 3200 mils. Check the students’ work. Repeat the exercise. See Instructors Notes Any Questions Questions from the class. Confirmation Questions to the class on using the RA protractor. What is the Grid Bearing from GR ....................... to GR .................? ANSWER: .................................. What is the Grid Bearing from GR .................................... to GR ........................? ANSWER: ................................. MEASURING GRID BEARINGS 3200-0(6400) MILS To measure a Grid Bearing on a map. SLIDE 12/11 1. Draw a line at least 8 centimetres long, as before. 2. With the Straight edge of the protractor to the right, place the centre point at one end of the line, making the scale or Romer lines parallel to the North-South grid lines. 12-5 3. Practise Read the bearing as before, but use the INNER SCALE because the bearing is between 3200 and 0 (6400) mils. Give the class two grid references and ask them to find the Grid Bearing from one to the other. Ensure that the bearing is between 3200 - 0 (6400) mils. Check the students’ work. Repeat the exercise. See Instructors Notes Any Questions Questions from the class. Confirmation Questions to the class on measuring Grid Bearings. What is the Grid Bearing from GR ................ to GR .......................? ANSWER: ................................. What is the Grid Bearing from GR ................ to GR .......................? ANSWER: ................................. PLOTTING A GRID BEARING To plot a Grid Bearing on a map. 1. 0(6400)-3200 MILS PLOTTING A GRID BEARING Measure the Magnetic Bearing, apply the GMA correctly to obtain the Grid Bearing. SLIDE 12/12 2. Place the centre point hole over the known map position with the straight edge to the left, and the scale and Romer lines parallel to the North-South grid lines. 3. Find the Grid Bearing on the outer scale and mark it on the map with a fine pencil. 4. Remove the protractor and use the straight edge to draw a line from the known position to the fine pencil mark. 5. The feature you want will be along this line. To plot a Grid Bearing on a map. Follow the procedure above except: 3200-0(6400) MILS SLIDE 12/13 Place the protractor along the straight edge to the right and read the Grid Bearing off the inner scale. Note: If you can estimate how far away the feature is, plotting a Grid Bearing will help you identify it on the map. Practise 1. What is the conventional sign ..... km away from GR ........... on a bearing of .......... mils (0 - 3200 mils)? ANSWER ................................. 2. What is the conventional sign .......................... km from GR ........... on a bearing of ..................... mils (3200 - 0 mils)? ANSWER ................................. See Instructors Notes 12-6 Any Questions Questions from the class. Confirmation Questions to the class on plotting Grid Bearings. At GR .................. a patrol is seen on a compass bearing of ............. mils and an estimated distance of ............................ What is the Full Grid Reference of the patrol’s position? ANSWER ................................. END OF LESSON Any questions Questions from the class on the whole lesson. Test on the Whole Lesson Write down the answers to the following questions. 1. What is the grid reference of the .......................... in the SouthWest corner of your map? ANSWER ................................. 2. What is the conventional sign ............................. km away from GR ............................ on a bearing of .......................... mils? ANSWER ................................. 3. What is the Grid Bearing between GR .............................. and GR ................................? ANSWER................................. Pack Equipment Pass answer papers to the front. Hand in stores. Summary Using a Romer will enable you to obtain exactly the same grid reference every time. Using the RA protractor enables you to take and plot bearings on a map to an accuracy of 10 mils. Using the attached string on the RA Protractor enables you to take bearings in adverse conditions, when wearing protective clothing and gloves. Look Forward In the next lesson you will be taught how to use the prismatic compass. INSTRUCTORS NOTES 1. Instructors must select and check sufficient examples and test questions before the lesson. 2. Note that the Yard Romers (Right Hand Side) are NEVER used. Normally tape or marker hide these Romers. 3. The RA Protractor usually has a thin string attached to the pivot to help take bearings. Although not covered in this lesson, instructors can easily bring its use into their instruction. 4. A new RA protractor is due to be issued around year 2001/2. 12-7