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V. SPEAKING

Task 1. Read the text and render its main ideas according to
the following plan.

1. Mistakes in measurements. Their causes.
2. Errors.

3. Types of errors.
4. Surveying methods rating.
No measurement can be perfect or exact because of the physical

limitations of the measuring instrument as well as limits in human
perception. The difference between a measured distance or angle and
its true value may be due to mistakes and/or errors. These are two

distinct terms. It is necessary to eliminate all mistakes and to minimize
all errors when conducting a survey of any type.
A blunder is a significant mistake caused by human errors. It may
also be called a gross error. Generally, it is due to the inattention or

carelessness of the surveyor and it usually results in a large difference
between the observed or recorded quantity and the actual or the true
value.

Mistakes may be caused by sighting on a wrong target with the
transit when measuring an angle, or by tapping to an incorrect station.
They also may be caused by omitting a vital piece of information,

such as the fact that a certain measurement was made on a steep slope
instead of horizontally. The possibilities for mistakes are almost
endless. However, they are only caused by occasional lapses of
attention.

An error is the difference between a measured quantity and its
true value, caused by imperfection in the measuring instrument, by the
method of measurement, by natural factors such as temperature, or by

random variation in human observation. It is not a mistake due to
carelessness. Errors can never be completely eliminated, but they can
be minimized by using certain instruments and field procedures and
by applying computed correction factors.

Using appropriate statistical formulas, it is possible to test and
determine the probability of different ranges of random errors

occurring for a variety of surveying instruments and procedures. The
most probable error is that which has an equal chance (50 percent)
of either being exceeded or not being exceeded in a particular

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