Page 25 - 4798

3.3.2 Overview of Mistakes and Errors
 Blunders can, and must, be eliminated.
 Systematic errors may accumulate to cause very large errors in the final
results.
 Accidental errors are always present, and they control the quality of the
survey.
 Accidental errors of the same kind accumulate in proportion to the
square root of the number of observations in which they are found.

3.4 Accuracy and Precision
Accuracy and precision are two distinctly different terms, which are of
importance in surveying. Surveying measurements must be made with an
appropriate degree of precision in order to provide a suitable level of accuracy for
the problem at hand.
Since no measurement is perfect, the quality of result obtained must be
characterized by some numerical standard of accuracy.
Accuracy refers to the degree of perfection obtained in the measurement or
how close the measurement is to the true value. When the accuracy of a survey is
to be improved or increased, we say that greater precision must be used.
Precision refers to the degree of perfection used in the instruments, methods,
and observations- in other word, to the level of refinement and care of the survey.
In summary:
Precision – Degree of perfection used in the survey. Accuracy – Degree of
perfection obtained in the results.
In a series of independent measurements of the same quantity, the closer each
measurement is to the average value, the better is the precision. High precision is
costly but is generally necessary for high accuracy. The essential art of surveying
is the ability to obtain the data required, with a specific degree of accuracy, at the
lowest cost. The specified degree of accuracy depends on the type and the purpose
of the survey.

23