The standard deviation within subgroups, which is an estimate of the variation within subgroups (for example, one shift, one operator, or one material batch). This value equals the estimated standard deviation for the R or S chart.
The standard deviation between subgroups, or an estimate of the variation between subgroups (for example, subgroups collected at set intervals, batches, or by different operators).
where batch size is the mode of the subgroup sizes.
If you specify a historical between standard deviation, then
estimated standard deviation for the I and MR charts (average moving range is the default)
The between/within standard deviation, combining within and between variation.
For more information about the I-MR-R/S chart, see Janis 1.
1 S. J. Janis (1990). "Is your process too good for its control limits?", 44th ASQC Annual Quality Congress Transactions, San Francisco, CA, 1006-1011.