الفهرس 
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Abstract
Errors may arise from the imperfections of measuring devices, from irregularities of atmospheric conditions, and from human influences.
This thesis is basically devoted to investigate the different techniques of directions observation and the errors that arise in these techniques, in order to achieve higher accuracies and best results in that phase by treating such errors and eliminating or minimizing their effect.
A theatrical study on theodolites and their adjustment is performed and the main sources of instrumental errors and their effect is discussed. Different techniques of directions observation and their accuracy and adjustment are presented.
This thesis includes a study of errors which arising in directions observation as well as a study of atmospheric refraction and its effect on directions observation.
A practical field work was carried out for representations and determination the element of atmospheric refracting and the correlative relations between the atmospheric refraction and the arising systematic errors in directions observation.
The representations and analysis of results are presented graphically and in tabulated form.
Many useful recommendations and conclusions are stated.