Control chart constants for X-bar, R, S, Individuals (called "X" or "I" charts), and MR (Moving Range) Charts.
NOTES: To construct the "X" and "MR" charts (these are companions) we compute the Moving Ranges as:
= range of 1st and 2nd observations, R
= range of 2nd and 3rd observations, R
= range of 3rd and 4th
observations, etc. with the "average" moving range or "MR-bar" being the average of these ranges with the
"sample size" for each of these ranges being n = 2 since each is based on consecutive observations ... this
should provide an estimated standard deviation (needed for the "I" chart) of
σ = (MR-bar)/d
where the value of d
is based on, as just stated, m = 2.
Similarly, the UCL and LCL for the MR chart will be: UCL = D
(MR-bar) and LCL = D
but, since D
= 0 when n = 0 (or, more accurately, is "not applicable") there will be no LCL for the MR chart,
just a UCL.