Operator‘s Manual FERITSCOPE
®
FMP30
Page 219
Glossary
conditions is a measure for the repeatability. The smaller the standard
deviation of these measurements, the better is repeatability. The repeat-
ability is dependent on the test method and the quality of the instrument,
but often also on the properties of the specimen (e.g., surface rough-
ness). The standard deviation of the measurements under repeatability
conditions can be reduced by generating the mean value of the mea-
surements (such as in auto-averaging mode). (
(Specification limits) Specification limits (LSL and USL)
mation, see / 20 /.)
Reproducibility
The ability of different operators to achieve practically the same mea-
surement result, when taking measurements with different instruments at
the same measuring position of the same specimen at different loca-
tions. (
Tolerance limits (Specification limits) Specification limits (LSL
and USL); for detailed information, see / 20 /.)
s
The standard deviation s is a measure of the deviations of single mea-
surements of a measurement series from their common mean value. It is
equal to the mean square deviation of the single measurements from the
mean value and is calculated as follows:
where:
s
= standard deviation
Fe.
= mean value of all single readings
Fe
i
= single readings
N
= number of readings
Figure 16.8 demonstrates that two measurement series with different
s
Fe. Fe
1
–
2
Fe. Fe
2
–
2
...
Fe. Fe
N
–
2
+
+
+
N 1
–
-----------------------------------------------------------------------------------------------------------------------
=