![]() ![]() Plotting a grid using the 1:50000 scale romer on the RA Protractor. Choose two points on a map and practice this procedure. Read of the inner scale and plot a bearing of 4500 mils back to the trig point. Protractors without the conversion formula will provide a reading that is off the exact grid coordinate position. To plot a backbearing from the church, turn the protractor to the left with the centre point over the church. One in my collection had been re- packaged (in polythene) in December 1976. The RM Military Protractor is the only protractor with a printed formula and a diagram to align map grid north to match the compass magnetic north. It remained in service long enough to acquire a NATO number W10 6675- 99- 445- 2112. The scales on one side, from top to bottom are: yards 1 inch = 1 mile yards 1/4 inch = 1 mile miles 1/4 inch = 1 mile yards 1:20,000 metres 1/4 inch = 1 mile metres 1 inch = 1 mile. The last ones made, including those made by Blundell Rules Ltd, were made of un- reinforced PVC and renamed Protractor Rectangular 6” Opaque ‘A’ Mk 4. When you look at your map you’ll notice that the MGRS lines and the Latitude/Longitude lines won’t match up. ![]() Later ivorine ones were not reinforced and the one pictured above is one of those. The Military Grid Reference System is a geographic coordinate system that comes from the Universal Transverse Mercator (UTM) grid system, which is based on a flat world, not a sphere. What materials are military protractors typically made from Military protractors are often made from durable plastic or acrylic for long-lasting use in the field. The earliest ones were reinforced in the ivorine with metal mesh and carried the patent number 361012/30 so it presumably replaced the AIII about 1930. How accurate is a military protractor A military protractor is designed for precise measurement and plotting, offering high accuracy. Later protractors were transparent and semi- circular. IMPROVED MILITARY MAP PROTRACTORS The current square issue map protractor is cumbersome to use, resulting in added time in planning, and inherently inaccurate resulting in map errors that can cause units to get lost and rounds to fall on friendly forces. The A Mk IV was the last, special design of British military rectangular protractor. Protractor Rectangular 6 inch Ivorine A Mk IV. ![]()
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