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We have two kinds of errors, random and systematic. My reaction time,
while using a stopwatch, will create a random error of +/- 0.2 seconds
but a reproducible systematic error will often be much larger, if the
instrument is too slow or too fast. I remember reading somewhere that
the terms precision and accuracy are used to make this distinction. The
term resolution, often used in optics, has to do with the ability of
distinguishing details, for example, in the case of "empty
magnification", or in the case of two nearly overlapping peaks.
If my use of the word "accuracy" is correct (Michael Edmiston used it in
the same way) then what is quoted below is not correct. Precision does
not contribute to the accuracy.
Ludwik Kowalski
Robert Cohen wrote:
...While I'm on the topic, I should mention that I will
be emphasizing the distinction between precision and
resolution and that both contribute to the accuracy of
the measurement ....
On Mon, 30 Aug 1999, Leigh Palmer wrote:
[snip]
The best treatment I found is in Bevington(d) and Robinson (Data
Reduction and Error Analysis for the Physical Sciences). I quote (with
asterisks enclosing *italics*):
Accuracy versus Precision
It is important to distinguish between the terms *accuracy* and
*precision*. The *accuracy* of an experiment is a measure of how
close the result of the experiment is to the true value. Therefore,
it is a measure of the correctness of the result. The *precision*
of an experiment is a measure of how well the result has been
determined, without reference to its agreement with the true value.
The precision is also a measure of the reproducibility of the
result. The distinction between the accuracy and the precision of
a set of measurements is illustrated in Figure 1.1 [sorry - Leigh].
*Absolute precision* indicates the magnitude of the uncertainty in
the result in the same units as the result. *Relative precision*
indicates the uncertainty in terms of a fraction of the value of
the result.
It is obvious that we must consider the accuracy and precision
simultaneously for any experiment. It would be a waste of time
and energy to determine a result with high precision if we knew
that the result would be highly inaccurate. Conversely, a result
cannot be considered to be extremely accurate if the precision is
low. In general, when we quote the *uncertainty* in an
experimental result, we are referring to the *precision* with
which that result has been determined.