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A Simple height and depth measuring instrument
Practical Action
Use of the instrument
1. Pace or measure a known distance from a point vertically below the point on the object
whose height is to be measured.
2. Take a plumb bob and pass the free end of the string through the hole in the vertical
strip corresponding to this distance. Tie a knot in the string at the rear of the hole to
prevent it from slipping out.
3. Standing at this known distance from the object to be measured, sight the top of the
object by eye along the top of the ruler (Fig. 2). Allow the string with the weight on its
end to move freely, under gravity, between the flexible strip and the ruler.
4. When the string has stopped swinging, clamp it by trapping it between the flexible strip
and the ruler with finger and thumb. Read off the height on the ruler's upper edge in the
same units used to measure the horizontal distance set on the vertical strip. If '6' on the
vertical strip represented 6 yards then '2' on the ruler will mean a height of 2 yards.
Figure 2: Using the measuring instrument.
There is always the possibility of the ground sloping between your viewing position and the base
of the object. It is as well, therefore, to take a second reading - the depth reading - which also
adds your eye level height to the measurement.
Depth reading
Turn the instrument around and look down from point A (Fig. 2) to the point vertically below the
point on the object being measured. Again, trap the string when the weight is stationary and read
off the ruler the depth of the base of the object below your eye level. Add this to the reading of
height and you will obtain the total height of the object from its base.