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Fig. 327.—Example of scale of shades for slopes.
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711.—Military Sketching Board.—This sketching board, Fig. 328, the invention of Mr. Graham F. Hodgson, will be found a very great improvement upon the old pattern boards. It is designed to meet the requirements of military and other officers not conversant with the higher branches of surveying, and it will also be found of great use to surveyors, explorers, and other travellers.
It consists of a mahogany board revolving on a circular metal plate attached to a handle held in the operator's left hand.
Mounted on the metal plate is a compass, which is visible through a glass plate flush with the face of the board and the tracing paper or cloth on which the map is made; the paper being stretched tightly over the board by means of rollers.
A magnetic north line is drawn on the paper over the centre of the compass. The operator invariably has his board in its relatively correct position by always keeping the magnetic north line immediately over the top of and aligned with the compass needle when his sights are taken.
Top view.