Presswell Notes.

Auckland Star, Volume LXIV, Issue 204, 30 August 1933, Page 16

Presswell Notes.

THE PRISMATIC COMPAS. ITS USE IN DISTANCE JUDGING. " Presswell" to-day preeents one of the most interesting methods of judging distances. Because it involves the use of a prismatic compass its use will be limited to those who are fortunate enough to have such an instrument available to them. However, every outdoor scout hopes one day to be able to include a prismatic compass in his personal hiking kit, so may find it worth while to note the following explanation. The method may be briefly etatcd thus:— Take a shot at the distant object, move 100 yards at right angles to that bearing, and take another reading. i Subtract these two readings and divide J the result into 5700 which will give the distance in yards. No scout will be content to know this rule of thumb method alone, and as " Presswell" specialises in explaining tho why a« well as the how, the outdoor scout will read on. Fifty-seven degrees is the angle at the centre of any circle made by an arc which is equal to the radius of that circle. (Your maths, master will explain this.)

Now if the triangle ABC (in the accompanying sketch) is treated as a segment of a circle, wo see why 5700 is used in the calculation (57 X 100 yards). This method is near enough to accurate. Providing the included angle (A C B in the sketch) is between 5° and 20°, the distance arrived at would be up to 1-1 Oth in error. When the included angle at 100 yards is ujider 5° you should increase your distance until the reading is above s°. Naturally you then multiply the 57° by the total number of yards moved. Thus, your computation might be B7° X 360 yards — distance 7° (included angle) whereas had the included angle at 100 yards been s°, tho working would have been 67° X 10° = distenot 6°