Damon Pryor
Physics Notes
12/5/06
http://www.rit.edu/%7Euphysics/uncertainties/Uncertaintiespart1.html#2breturn
Systematic error
is the result of a miscalibrated device, or a measuring technique which
always makes the measured value larger (or smaller) than the "true" value.
Least count
is the smallest division that is marked on the instrument.
Instrument limit of error
,
ILE
for short, is the precision to which a measuring device
can be read, and is always equal to or smaller than the least count.
Estimated uncertainty
is an uncertainty estimated by the observer based on his or her
knowledge of the experiment and the equipment. This is in contrast to
ILE
,
standard
deviation
or
average deviation
. ???
The statistical method for finding a value with its uncertainty is to repeat the
measurement several times, find the
average
, and find either the
average deviation
or
the
standard deviation
.
To get a nonzero estimate of deviation we take the average of the absolute values of the
deviations, as shown in Column 3 of Table 1. We will call this the
average deviation
,
∆
t
.
The sum of the squares is divided by 3, (one less than the number of readings), and the
square root is taken to produce the sample
standard deviation
.
The proper way to write the answer is
1.
Choose the largest of (i) ILE, (ii) estimated uncertainty, and (iii) average
or standard deviation.
2.
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 Fall '07
 Wagner
 Physics, Normal Distribution, Standard Deviation, pH, 67%, 0.07 m/s

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