of the horizontal distance. For example (Fig. 9), if the apex reading is 41 % and the ground reading 13 %, the total height of the pillar measured from a distance of 25 m [82 ft] is (41 + 13) / 100 x 25 m = 54 / 100 x 25 m = ca. 13.5 m [(41 + 13)/100 x 82 ft = 54/100 x 82 ft = ca. 44 ½ ft].
When the pillar base is above eye level, the base reading is subtracted from the apex reading, and the total height is the difference percentage of the horizontal distance. For example (Fig. 10), if the apex reading is 64 % and the base reading 14 %, the total height is (64 – 14) / 100 x 25 m = 50 / 100 x 25 m = 12.5 m [(64 – 14) / 100 x 82 ft
=50 / 100 x 82 ft = 41 ft]. When calculations are made mentally, it is advisable to use measuring distances of 50, 100 or 200 ft, for the sake of simplicity.
12.5m [33½ ft]
3.5 m | 64% |
[11½ ft] |
|
| 14% |
25 m [82 ft]
Fig. 10. Pillar above eye level
14
