(2) Treatment.
(a) Proper training and motivation of operators.
(b) Check equipment prior to use.
(c) Exercise care in operating equipment.
(d) Follow valid (written) procedures.
(e) Be alert for unusual readings or conditions.
(3) Allowance.
Since this type of error cannot be predicted, no
allowance can be made however, a second setup or additional readings will
usually reveal it.
c. Systematic errors.
Systematic errors, sometimes called persistent
errors, tend to bias all the measurements in one direction. Causes of this
type error can be located and reduced if some standard is available to
compare the mean of the measurements against, or if by substituting other
methods and/or equipment, the mean of the measurement's changes as a result
of the substitution.
This type error may be either observational,
environmental, or instrumental.
(1) Observational errors.
(a) General.
Since the observer is human, most observational
errors grow out of human factors. This is the one area of measurement where
subjectivity enters the picture.
(b) Scale. If the scale is poorly printed, it is a fault of the
instrument; but if it is poorly read, this is a fault of the observer. This
is a prevalent source of error.
(c) Parallax.
There is a finite distance between the needle and
the scale. If readings are made from different angles, different readings
will be obtained, and there is no way to tell which one is correct.
(d) Interpolation. When the needle is not exactly on a division
mark, the observer has to estimate just what the reading is in the last
decimal place.
(e) Calling.
When values are read by one person and called to
another person to write down, there can be speaking errors, hearing errors,
and writing errors. Sometimes calling is necessary when several values must
be read simultaneously.
(f) Memory. Trusting the value of a reading to memory for a short
period of time can lead to errors. We tend to see things as we
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