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6. Test to see if the compensator is working.
7. Remove parallax (the shift in position of an object caused by
your own motion).
Once the level is set up its important that the line of sight is

horizontal. If the line of sight is not horizontal when the instrument
has been levelled, the level has a collimation error.
As most levels will have some level of collimation error, a

method is required to check if the error is within acceptable limits.

Task 3. Answer the questions, using the active vocabulary.
1. What is levelling? What does it measure?

2. How are heights defined?
3. What is a bench mark?
4. What is the direction of gravity?

5. What steps are taken when using a level?
6. When does a collimation error occur?

Task 4. Define whether the following statements are true or
false. Correct the false ones according to the text:

1. It is impossible when levelling to measure heights with an
accuracy of millimeters.

2. The height of a point is measured along the vertical only
above the chosen datum.
3. On most construction sites there is a permanent datum.
4. If heights are based on an arbitrary datum these are known

as Permanent Bench Marks or PBMs.
5. Over large areas, as the Earth is curved, level surfaces will

also be curved.
6. One of the most popular ways to measure heights is using a
level.
Gyrotheodolite

Task 1. Read and memorize the following words and word-
combinations:

Gyrotheodolite – гіротеодоліт;
to be composed of – складатися з;
to locate the meridian direction – визначити напрямок
меридіана;

mine surveying – маркшейдерське знімання;

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