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Prerequisites
Calculations
1
Statistical calculations
For all numerical calculations necessary in this quality control manual the testing
person should use the formulae indicated in the following text together with a pocket
calculator or appropriate software for numerical evaluations.
Preliminaries:
From the knowledge of any finite set of measurement values x
following fundamental statistical quantities can be established.
1.1 Global average of values
x
= each value (e.g. x
N
N = number of measurement values (e.g. 6, for 6 PMMA thicknesses)
x
= global average of values
av
1.2 Standard deviation
= standard deviation
σ
x
With the average value x
1.3 Coefficient of variation
c
= coefficient of variation
var, x
With the average value x
Global average of values and Standard deviation respectively.
12
x
+
x
1
2
-------------------------------------------------- -
x
=
av
= value of pixel 1, x
1
1
2
--- -
σ
=
⋅
(
(
x
–
x
)
+
(
x
x
1
av
2
N
calculated according to Global average of values.
av
c
var,x
and the standard deviation σ
av
+
x
+
...
+
x
3
N
N
= value of pixel 2)
2
2
2
–
x
)
+
...
+
(
x
–
x
)
)
av
N
av
σ
x
------ -
=
x
av
calculated according to
x
, x
, ..., x
the
1
2
N
Quality Control Manual
SPB7-330.640.01.01.02
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