Hach-Lange TITRALAB 860_865 Reference Manual - Manual (Page 238)

Titra Lab ® TitraLab 860 and 865 Reference Manual
Page 238
3. Standard deviation calculation
For every result obtained on several aliquots, a mean value is calculated with which a standard
deviation is associated.
Definitions:
R
i
= Result of test i
Mean result:
Standard deviation on the mean value
σ
µ
:
- Number of tests N = 2 to 5 : estimation of the Q variance for a small number of tests.
with R
max
= maximum value of the R
i
and R
min
= minimum value of the R
i
:
- Number of tests N > 5
Result is expressed with the mean value R and the standard deviation
σ
µ
on the mean value:
Result = R ±
σ
µ
N Q
2 1.128
3 1.693
4 2.059
5 2.326
¦
=
n
i n
R SR
1
¦
=
n
i n
R SR
1
2
2
N
SR
R n =
N
Q
R R
2
min max
2
¸¸¹
·
¨¨©
§ −
=
µ
σ
( )
N N
N
SR
SR n
n
µ × −
−
=
1
2
2
2 σ