# Mapric lesson 12

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```							                                                                                              LESSON 12

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.

Projector and Screen                        5.      Read the Instructors Notes before the
lesson.
Time Allowed:
2.      Check RA Protractors New/Old.
40 Minutes
3.      ...........................................................

4.      ...........................................................

12-1
BEGINNING OF LESSON
STAGE                                  CONTENT
Revision      Write down the grid references of the four places of worship shown on
the slide.
SLIDE 12/1
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                What is a Romer?
LIGHTWEIGHT        A Romer is a device which you can use to accurately divide a grid
COMPASS            square into 10 equal parts in Eastings and Northings.
ROMER
How is a Romer used?
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     DEMONSTRATE how to take a grid reference from a map using a
REFERENCE          Romer.
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.
The grid reference actually identifies the bottom left-hand, or South-
100 Metre Square   West 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     DEMONSTRATE how to plot a grid reference on a map using a
REFERENCE          Romer.
USING THE

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    The RA protractor is the standard issue protractor. It is used for plotting
TO THE RA       and measuring bearings, measuring distances, and for giving accurate
PROTRACTOR      grid reference by means of the Romers.
RA              Pick up your protractor and find the 1:50,000 Romer.
PROTRACTOR                             SLIDE 12/7
ROMERS
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    The main use of the RA protractor is to measure and plot Grid
PROTRACTOR      Bearings:
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           To measure a Grid Bearing on a map.
GRID BEARINGS                                   See Instructors Notes
SLIDE 12/10
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.
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 .................?
What is the Grid Bearing from GR .................................... to GR
........................?
MEASURING           To measure a Grid Bearing on a map.
GRID BEARINGS                           SLIDE 12/11
1.       Draw a line at least 8 centimetres long, as before.
3200-0(6400) MILS   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.       Read the bearing as before, but use the INNER SCALE because
the bearing is between 3200 and 0 (6400) 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 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 .......................?
What is the Grid Bearing from GR ................ to GR .......................?
PLOTTING A          To plot a Grid Bearing on a map.
GRID BEARING        1.       Measure the Magnetic Bearing, apply the GMA correctly to
obtain the Grid Bearing.
0(6400)-3200 MILS                                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.
PLOTTING A          To plot a Grid Bearing on a map.
GRID BEARING        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
Practise            1.       What is the conventional sign ..... km away from GR ...........
on a bearing of .......... mils (0 - 3200 mils)?
2.          What is the conventional sign .......................... km from GR
........... on a bearing of ..................... mils (3200 - 0 mils)?
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?

END OF LESSON
Any questions            Questions from the class on the whole lesson.
Test on the Whole        Write down the answers to the following questions.
Lesson                   1.     What is the grid reference of the .......................... in the South-
2.    What is the conventional sign ............................. km away
from GR ............................ on a bearing of .......................... mils?
3.      What is the Grid Bearing between GR .............................. and
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

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