User`s manual

Formula Variables
SPC Formulas
Statistical process control makes use of numerous formulas,
and those that pertain to the SPC option of the support
software are included in this appendix, along with the
definitions of the variables used in these formulas.
Here is a list of the variables used in the SPC formulas.
1.
x = an individual observation or inspection result.
2.
x (x bar) = the average of a series of individual
observations.
3.
F (x double bar) = the average of the < values.
4.
n = the number of observations in a subgroup.
5.
k = the number of subgroups.
6.
R = the difference between the maximum and
minimum x values in a subgroup.
7.
i? (R bar) = the average of the R (Range) values of the
subgroups.
8.
0 = the standard deviation of a population.
9.
s = the standard deviation of a sample.
10. s (s bar) = the average of the s values of the subgroups.
11. p = the fraction of non-conforming units in a subgroup.
12. i (p bar) = the average fraction of non-conforming
UUitS.