(36) T = C{T(V) - T(v)}.
Denoting the angle of departure and descent, measured in degrees and from the line of sight OB by φ and β, the total deviation in the range OB is (fig. 1)
(37) δ = φ + β = C{D(V) - D(v)}.
To share the δ between φ and β, the vertex A is taken as the point of half-time (and therefore beyond half-range, because of the continual diminution of the velocity), and the velocity v0 at A is calculated from the formula
| (38) T(v0) = T(V) - | ½T | = ½{T(V) + T(v)}; |
| C |
and now the degree table for D(v) gives
(39) φ = C{D(V) - D(v0)},
(40) β = C{D(v0) - D(v)}.
This value of φ is the tangent elevation (T.E.); the quadrant elevation (Q.E.) is φ - S, where S is the angular depression of the line of sight OB; and if O is h ft. vertical above B, the angle S at a range of R yds. is given by
(41) sin S = h/3R,