Dynalyzer – Digital Display/Printer OPERATION MANUAL
19
COV values to within 0.004 of the actual computational value can be attained. The formula
employed in the internal calculation is as follows:
Where:
• C = Coefficient of Variation
• X = Mean value of displayed parameter
• X
i
= “i” th value
• N = population of observations and thus, with “n” equal to 10
In running these tests the user should take care not to overheat the x-ray tube anode.
If an improper or totally erroneous exposure was made during a statistical run, the CLEAR
READING and EXPOSURE RECALL pushbuttons may be depressed. This clears out that value,
and resets the exposure counter by one. The test may then be resumed.
Exposure recall allows viewing the data stored for each of the ten exposures. This allows the
possible source of the error to be seen if the COV is high.
It should be pointed out that the only parameter that requires COV measurement is the R output
for BRH acceptance tests. By displaying the COV of the other parameters the cause of various
problems can be isolated.
If fewer than 10 exposures are made, an error indication of “909” will appear in the
PERCENT/PRESET display window. When this occurs, the unit will still calculate the COV value,
but it must be remembered that this does not satisfy the DHHS requirement of 10 exposures.
C=
x
1
[ ]
2
i
(x - x)
n-1
i=1
n
2
1
i=1
10
x
i
10
1
=
x
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