Metrohm 899 Coulometer - Manual (Page 114)

10.9 Arithmetic algorithms in the 899 Coulometer
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899 Coulometer
Statistics
The arithmetic mean value and the absolute and relative standard devia-
tions of results are calculated:
You can statistically evaluate a maximum of five results (1 ≤ k ≤ 5) calcula-
ted in a determination. A statistical series can contain a maximum of 20
determinations (1
≤ n ≤ 20).
The following convention applies to the subsequent formulas:
1 ≤ n ≤ 20 and 1 ≤ k ≤ 5.
Mean value:
Absolute standard deviation:
Relative standard deviation (in %):
Explanations
The individual values are incorporated in the statistics with full accuracy.
15 significant places are yielded when the 64 bit numerical format is
applied for the floating-point number in decimal presentation.
The accuracy can be controlled by the selection of the prefix of the unit
(milli, micro) and the number of decimal places.
Example:
The result displayed, 1234.56789158763 mg/L, has 15 significant pla-
ces. It should be rounded off to three decimal places according to the
above rounding-off process:
￭ 1234.568 mg/L.
If the same result is expressed in "g/L" (1.23456789158763 g/L), and is
also rounded off to three decimal place, this yields
￭ 1.235 g/L.
I.e. you obtain the lowest losses in accuracy with rounding when you
select the application and the numerical format in such a way that the
numbers displayed have as many places before the decimal point as possi-
ble.
A complete recalculation of the statistics using a pocket calculator or PC
calculation programs may exhibit deviations. This can be explained by the
different binary numerical formats used by these computers.