As promised in the previous post, some scans
on the angle measuring instructions that came with my “Italian Army” compass.
The first paragraph refers to the clinometer. If you work in certain fields the
contents of column V will be familiar to you. This column can be read as either
fractions or gradients. That is, for example, 25% = ¼ = 1 in 4. A slope of 14°
therefore drops or rises one metre for every four metres of horizontal
distance. A 45° slope is 1/1 so changes by a metre for every horizontal metre.
In the illustrated example below a hilltop
is measures as being at 14° to the viewer so its height must be a quarter of
the distance between the two. The converse is also true. If you know the height
of an object and can measure the angle you can calculate the distance. A
building storey is 3 metres so a three story building will be 9 metres. If the
observed angle to the top of the third storey is 6° then the distance must be 90
(9 x 10) metres.
The same system can be used with
horizontal angles, taken from bearings of each side of an object. Also
illustrated is a way to use the graduations on the window in the cover to
calculate the distance from an object of known width.
The Books
