(2) The gathering of data holds a key position in the scientific
method and in metrology.
In measurement, most data are numerical values
taken from a calibrated dial or scale of some sort, and usually by means of
some interpolation.
Certain scales are easier to read than others.
The
National Bureau of Standards recommends (for electrical meters) a knife edge
pointer with the thickness of the knife edge equal to that of the division
lines, and preferably of a size not more than one-tenth the distance between
two successive scale division marks. The scale division marks should be at
least 1 mm apart. Such a scale equipped with an antiparallax mirror can be
estimated to one-tenth of a division.
Certain types of scales can be
equipped with a vernier to make possible a finer reading.
The 10/1000
micrometer is an example of splitting the division into tenths.
Certain
clinometers have a vernier, which makes possible the splitting of degrees
into minutes, each of which is one-sixtieth of a division. An outstanding
example of the vernier principle is found in optical proving rings, where
divisions one one-thousandth of an inch apart can be read to one one-
hundredth part of a division.
(3) Observational errors usually result from misreading the scale,
failure to eliminate parallax, and failure to estimate fractional divisions
correctly.
f. Data.
(1) Raw data.
Raw data are of little value.
Before their full
meaning is apparent, the conditions under which they were obtained must be
known and they must be recorded, manipulated statistically, interpreted and
evaluated, and put into a suitable form for presentation.
They should be
recorded as soon as possible to avoid the danger of forgetting. Unless a
prepared form is available, the data should be clearly labeled to include
all pertinent circumstances.
Raw data are seldom of much value until all
systematic errors are allowed for and the random errors averaged out by some
statistical process. When it is finally determined to be the best guess of
the value in question, there is still the problem of how good is the guess.
In other words, what is the probability that it is completely correct.
(2) Evaluating data.
Data is nothing more or less than just plain
information. Data may be true or false, accurate or inaccurate. The job of
the calibration specialist is to obtain data and to evaluate its validity.
(3) Recording data.
(a) General.
Data should be recorded as soon as possible.
Objective information left to memory, even for a short while, starts to lose
its objectivity.
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