Manual of military engineering . length. 316. To make a section with such rods, it is usual to select thehighest point of the section and there drive in a picket flush withthe ground, driving in a second picket on the line of the sectionwith its top carefully levelled to the top of the first picket (bymeans of the field, masons, or spirit level), and as far awayfrom the first picket as the length of the level or straightedge\\dll allow {see A, B, Fig. 3, PL 83). It is evident then by look-ing over the tops of the two pickets (A, B), the depth belowthe line of sight of any other points (C, D),

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Manual of military engineering . length. 316. To make a section with such rods, it is usual to select thehighest point of the section and there drive in a picket flush withthe ground, driving in a second picket on the line of the sectionwith its top carefully levelled to the top of the first picket (bymeans of the field, masons, or spirit level), and as far awayfrom the first picket as the length of the level or straightedge\\dll allow {see A, B, Fig. 3, PL 83). It is evident then by look-ing over the tops of the two pickets (A, B), the depth belowthe line of sight of any other points (C, D), on the section couldbe determined by holding up a measuring rod at those points,and the horizontal distance apart of the various points beingalso measured, a rough section could be made. To avoid theobvious difficulty of getting ones eye down to the top of thefirst two pickets (A, B), boning rods are set up on them, anda third boning rod (or the long rod) is set up at the different :Plcxjtie< (S3 BONING & LEVELLING -Z^.^.. ^ s

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