4. There are many good ways to measure distances. The method of measurement you use will depend on several factors:
In the following sections, you will learn how to use the various methods of measurement. Table 1 will also help you to compare these methods and to select the one best suited to your needs.
2.1 How to measure short distances with a ruler1. To measure short distances, use a measuring stick called a ruler, 4 to 5 m long. You can make your own by following the steps below. A ruler is particularly useful for measuring horizontal distances on sloping ground. Making your own ruler2. Get a piece of wood which is straight and flat. It should be about 5 cm wide, and a little more than 4 m long. You can also use a shorter length, if the distance you are going to measure is shorter. 3. It is best to use a planed piece of wood, but if you cannot get one you may use a straight wooden pole. If you use a pole, you should plane at least one of its surfaces.
4. You should now add graduations to it. Graduations are marks which show exact measurements, in centimetres, decimetres, metres, etc. To do this, you need to get two ready-made measuring tapes, such as the 2 m ribbon tapes that tailors use. Glue one of these measuring tapes onto the planed face of your piece of wood. Take care to align the zero mark of this tape with one of the ends of the piece of wood. Glue the second tape next to the end of the first tape; this should reach near the end of the piece of wood. Drive several small nails through the tapes to secure them better. 5. You can also make the graduations yourself. Using a measuring ruler or tape, mark the graduations on the piece of wood with a pencil. With a knife or saw, make a straight, shallow cut every 10 cm. A carpenter, with his tools, can help you to do this more accurately. Identify the graduations with numbers (for example, every 0.5 m) using paint or ink; or you can use a piece of hot wire to burn the graduations and their numbers into the wood.
2.2 How to measure distances by pacing1. You may measure distances roughly by pacing. This means you count the number of normal steps which will cover the distance between two points along a straight line. Pacing is particularly useful in reconnaissance surveys, for contouring using the grid method (see Section 8.3) and for quickly checking chaining measurements (see Sections 2.3 to 2.5). 2. To be accurate, you should know the average length of your step when you walk normally. This length is called your normal pace. Always measure your pace from the toes of the foot behind to the toes of the foot in front.
Finding your own pace factor3. To measure the average length of your normal pace (the pace factor, or PF):
Measuring horizontal distances with a steel band or a tape3. Plot the straight lines you need to measure. If the lines are the same length as your measuring band or tape or shorter, you can measure the distances directly. To do this, stretch the band or tape from one peg to the next one. 4. If the lines are longer than your band or tape, use one of the methods described later (see Section 2.6). Note: you should pull bands and tapes tight, so that they do not sag, especially when you are measuring long distances. But, you should avoid over-stretching them (especially fibreglass tapes), since this could lead to errors.
Measuring horizontal distances with a chain6. The chain is used for measuring the lengths of straight lines, which should be marked at each end with a ranging pole. You will need an assistant to help you. The method of chaining you use depends on the type of terrain you are measuring (see Section 2.6).
2.6 How to measure distances by chaining1. As you have learned, measuring lines can be ropes, bands, tapes or surveyor's chains. When you measure long distances, the way you use the measuring line will depend on the slope of the terrain. When the terrain is flat or nearly flat (that is, with a slope of 5 percent or less - see Section 4.0), you can measure the horizontal distances by following the ground surface. This method is usually used in measuring fish culture sites, where steeper slopes must be avoided. When the slope of the terrain is steeper than 5 percent, you should be especially careful when you measure the horizontal distances because in this case the surface measurement is always greater than the horizontal measurement.
21. As you measure on sloping ground, remember these important requirements:
Measuring distances on sloping ground26. If you are taking a measurement on a slope greater than 5 percent, you must correct the clisimeter reading to get the true horizontal distance. To do this, you need to use a mathematical formula, as explained in Section 4.0.
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