Question

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Trigonometric leveling

Trigonometric levelling consists in computing the difference in elevation of
two points on the basis of horizontal distance and the vertical angle between
them. It is usually combined with the triangulation work, the vertical angles being
measured at the same time as the horizontal angles, a vertical angle is
measured to some definite point on the signal the height of which above the
station was determined when the signal was erected. The height of the
instrument above its own station should also be measured and recorded. In a
very precise work angles are measured with a special vertical circle
instrument. In a less precise work an ordinary theodolite the vertical arc of
which reads to 50 sec. or to 20 sec. may be used but with such instruments only
single readings can be made. In this case the best results are obtained by
averaging several independent readings half of which are taken with the
telescope direct and other half with the telescope inverted.

The chief difficulty in obtaining accurate results by trigonometric levelling
is the uncertainty in the coefficient of refraction of the air. This varies
with locality, temperature and atmospheric pressure and the only way its effect
can be eliminated is by taking simultaneous observations between two
stations. 

Answer 1

1) Trigonometric levelling consists in computing the difference in elevation of
two points on the basis of horizontal distance and the vertical angle between
them, doesn't it?
2) Is it usually combined with the triangulation work, the vertical angles being
measured at the same time as the horizontal angles?
3) What is measured to some definite point on the signal the height of which above the station was determined when the signal was erected?
4) Should the height of the instrument above its own station also be measured and recorded?
5) Are in a very precise work angles measured with a special vertical circle
instrument?
6) Are the best results obtained by averaging several independent readings half of which are taken with the telescope direct and other half with the telescope inverted?
7) The chief difficulty in obtaining accurate results by trigonometric levelling
is the uncertainty in the coefficient of refraction of the air, isn't it?
8) What can be eliminated is by taking simultaneous observations between two
stations?
9)  What consists in computing the difference in elevation of two points on the basis of horizontal distance and the vertical angle between them?
10) What results are obtained by averaging several independent readings half of which are taken with the telescope direct and other half with the telescope inverted?