Home / Statistical Tools / Control Charts / S
S¶
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QXL Stat Tools Tab > Control Charts > Variables > Charts in Subgroups > S
This is a single panel of the Xbar-S chart
A S chart is the S Chart panel, the subgroup standard deviations, drawn on its own. It is not a separate analysis: the ribbon's S entry opens the Xbar-S Chart dialog with the S only radio already selected, and the dialog title still reads Xbar-S Chart.
Everything about the data it reads, the options it offers, and the way the limits are computed is described on Xbar-R and Xbar-S. This page covers only what is different when S only is the selected variant.
Want to build one first?
The walkthroughs live with the full chart: How-To builds one step by step from sample data you copy off the page straight into Excel, and How-To with GroupBy does the same with a grouping column. Both use both panels; switch the Chart: radio group to this variant at the same point in the steps to follow along here.
What is different under S only¶
- Only the lower panel is drawn. The Xbar panel is still computed, it is just not written to the worksheet, and it gets no row in the summary table either.
- Rules 5 through 8 grey out. Those four tests read the zones of the location panel, and on this variant there is no location panel left to test.
- Reference lines are never drawn. They attach to the location panel, so a reference line you enter here is accepted and then has nowhere to go.
- Fill the StdDev row of the manual limits grid, not the Xbar row. The Xbar row is still shown and still accepted, but that panel is not drawn.
- Use unbiased constants (within sigma) changes the shape of this panel, not just its width. Clearing it flattens the center line to a single value while the limits keep stepping with subgroup size. This is the only setting on either chart that does that, and on this variant the affected panel is the only one you can see.
Capability is unaffected by the panel choice
A capability analysis, when you ask for one, is computed from your individual measurements rather than from the plotted standard deviations, so it reads the same on this variant as on a full Xbar-S chart.
When to use it¶
- You want the subgroup standard deviations on their own, without the companion panel beside them.
- You are reading, printing or sharing one panel and the other would be noise.
If you want both panels, use Xbar-R and Xbar-S.
Output¶
The analysis writes one worksheet named S Chart. Under GroupBy there is one worksheet per group, each named S Chart - {GroupName}.
Worksheets are divided by GroupBy group, not by chart. Every chart belonging to a group is stacked down that one worksheet, one below the other, so selecting three measurement columns without GroupBy produces three charts on a single sheet rather than three sheets. The User Input block is written once at the top of each worksheet; everything after it repeats for each chart on the sheet.
The sheet holds the User Input block, the single S Chart panel, a summary table to its right covering that panel only, and, when you entered a specification limit or a target, a capability and histogram block below it. The full layout is described on Xbar-R and Xbar-S.
When the analysis finishes, the Control Chart task pane opens on the right. See Task Pane for what it can and cannot change.