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field must be checked by some independent field observation. The
following are the examples of mistakes:
1. erroneous recording, e.g. writing 69 in place of 96.
2. counting 8 for 3.

3. forgetting once chain length.
4. making mistakes in using a calculator.
Accidental Errors. Surveying errors can occur due to

unavoidable circumstances like variations in atmospheric conditions
which are entirely beyond the control of the observer. Errors in
surveying due to imperfection in measuring instruments and even
imperfection of eyesight fall in this category. They may be positive

and may change sign. They cannot be accounted for.
Systematic or Cumulative Errors. A systematic or cumulative
error is an error that, under the same conditions, will always be of the

same size and sign. A systematic error always follows some definite
mathematical or physical law and correction can be determined and
applied. Such errors are of constant character and are regarded as

positive or negative according to as they make the result great or
small. Their effect is, therefore, cumulative. For example, if a tape is P
cm short and if it is stretched N times, the total error in the

measurement of the length will be P´N cm.
Understanding the nature of random errors helps to understand
why systematic errors are never really fully corrected, since the
observation of the physical phenomena causing the error, or the

aligning and calibration of instruments in itself contains personal,
random errors. Thus, measurements have "uncertainties" or random
errors which remain unquantifiable. Random errors are dealt with by

controlling or managing them. It is a quality control process. They
cannot be corrected or eliminated, only minimized and controlled.
Random errors are unavoidable. They follow random patterns,
or the laws of "chance." They have unknown signs; thus, they are

expressed as "plus or minus." The magnitude of such an error is
unknown, but it can be estimated. These errors are caused by human
and instrument imperfections as well as uncertainties in determining

the effects of the environment on measurements.
The systematic errors may arise due to variations of
temperature, humidity, pressure, current velocity, curvature,

refraction, etc. and faulty setting or improper leveling of any

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