| Calculation
of gradients, using ratio
Marjorie
Henry, Contributor
In
the last lesson, I shared with you on the calculation of gradients using ratio.
I gave you an exercise on this concept and I do trust that you did it. I will
now go through the procedures for this exercise. | STEP
1 | - | Write
out the formula, that is, | VD
or DH
HD | | | | | | | STEP
2 | - | Calculate
the vertical difference:-
Height at trig station K8 = 232ft.
Height at trig
station K9 = 79ft.
Difference in height = 153ft. | | | | | | STEP
3 | - | Calculate
the horizontal distance:- Horizontal
distance
=
1,450 yds. X 3 = 4,350 ft. | | | | | | STEP
4 | - | Gradient
= | 153
4,350
| | | | | | | Answer=
1:28. | | | |
You
would have noticed that when you divided 4,350 by 153 that was equal to 28.43.
Since .43 is less than half of 153, this was disregarded. Today
I will continue the discussion of Question 1 from the recent examination (June
2007) by referring to part (f) of the question. It is as follows: (f)
Measure the bearing from the trigonometrical station K2 to the K1 station. Both
are located at the Golden Rock Airport. The
concept being tested here is that of STATING DIRECTIONS IN TERMS OF COMPASS BEARING.
Let
me remind you that directions in map reading are given in one of two ways, namely,
COMPASS DIRECTIONS and ANGULAR BEARINGS. In doing angular bearing, accuracy is
absolutely important. Make sure that you work with a sharp pointed pencil. Since
you have to use your protractors to measure the angle, I do trust that you know
how to use it and interpret the information. Angular
bearings are measured from north around towards the east, that is, in a clockwise
direction. It follows then, that the bearing of a point due east is 90º,
and of a point due west is 270º. Let us go back to the question and work
it through step by step. Since
you are asked to measure the bearing FROM the trig station K2, it is at that point
that you use your straight edge to draw a short vertical line to pass through
the station. You then draw another line from trig station K2 to K1. Next you place
your protractor along the vertical line at K2 and read the size of the angle formed
by the diagonal line drawn to K1. That would be 60º The answer to the question
then is 60º. Here
are two exercises for you to do. I trust that by doing them, you will understand
the concept better. 1.
Measure the bearing from the trig station K12 (218112) to K48 (232118). Both are
located along the coast. 2.
Measure the bearing from the trig station K9 (246130) to the Church at Pond Estate
(238125). Marjorie
Henry is an independent contributor. | 
