Derive X-bar and R center lines, control limits, and out-of-control flags from subgroup measurements. The workbook becomes the system of record; Apps Script owns the joins and business rules so analysts are not pasting monthly formulas.
Entry point `buildSpcControlData` reads typed columns with SpreadsheetApp batch APIs. SpreadsheetApp is the primary service; Time-driven describes how you usually invoke it after authorization.
Keep thresholds (grace days, bands, alert emails, API keys) in Config cells or Script Properties so the same .gs file promotes from sandbox to production without code edits.
This page is technical only: sheet layout, edge cases, runnable code, deploy steps, and FAQs for build spc x-bar and r chart data. No consulting pitch—just the pattern you can paste and harden.
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Sheet / project setup
| Tab | Columns | Notes |
|---|---|---|
| Measurements | Timestamp, Value | Raw |
| SpcData | Subgroup + limits | Chart data |
What this script does
buildSpcControlData() derive X-bar and R center lines, control limits, and out-of-control flags from subgroup measurements.
- Subgroup size 5
- A2/D4 constants
- XBAR_OOC / R_OOC flags
Prerequisites
Container-bound script on the workbook that contains the tabs in the setup table. Authorize SpreadsheetApp scopes on first run.
- V8 runtime
- Exact sheet names
- Script timezone = ops timezone
Walkthrough
Chunk measurements into subgroups of 5, compute X-bar/R, apply A2/D3/D4 constants, flag OOC points.
Paste the code, set Config/Properties, run buildSpcControlData once, verify the output tab, then attach a Time-driven trigger.
Edge cases
Trailing points that do not fill a full subgroup of 5 are dropped until more data arrives.
Testing
Use a sandbox copy with 3–5 known rows. Compute expected outputs for build spc x-bar and r chart data offline, run buildSpcControlData, and diff the output tab including one intentional bad row.
Hardening
Add LockService around multi-sheet writes if triggers can overlap. Log run timestamps. Keep API keys and alert emails in PropertiesService—not in shared cells.
Variations
Fork ideas: filter to one business unit, change grain (daily→weekly), or POST a summary payload after buildSpcControlData succeeds.
Operations notes
Assign an owner for the output tab, document regenerate steps, and treat `buildSpcControlData` as source of truth over ad-hoc cell formulas.
Full code: buildSpcControlData()
Run buildSpcControlData when source tabs are current. Edit sheet names and Config/Properties first.
function buildSpcControlData(){
const SUB=5; // subgroup size
const ss=SpreadsheetApp.getActive();
const vals=ss.getSheetByName('Measurements').getDataRange().getValues().slice(1).map(r=>Number(r[1]));
const groups=[];
for(let i=0;i+SUB<=vals.length;i+=SUB){
const g=vals.slice(i,i+SUB);
const mean=g.reduce((a,b)=>a+b,0)/SUB;
const range=Math.max.apply(null,g)-Math.min.apply(null,g);
groups.push({mean,range});
}
const xbar=groups.reduce((a,g)=>a+g.mean,0)/groups.length;
const rbar=groups.reduce((a,g)=>a+g.range,0)/groups.length;
const A2=0.577, D3=0, D4=2.114; // n=5
const uclX=xbar+A2*rbar, lclX=xbar-A2*rbar;
const uclR=D4*rbar, lclR=D3*rbar;
const out=groups.map((g,i)=>[
i+1,g.mean,g.range,xbar,uclX,lclX,rbar,uclR,lclR,
(g.mean>uclX||g.mean<lclX)?'XBAR_OOC': (g.range>uclR?'R_OOC':'OK')
]);
const sh=ss.getSheetByName('SpcData');
sh.clearContents();
sh.appendRow(['Subgroup','Xbar','R','CL_X','UCL_X','LCL_X','CL_R','UCL_R','LCL_R','Flag']);
if(out.length) sh.getRange(2,1,out.length+1,10).setValues(out);
}- Line 1: Entry point — bind triggers to buildSpcControlData.
- Line 4: Batch read; avoid per-cell getValue in loops.
- Line 24: Batch write output rows in one setValues call.
- Line 5: Rename sheet constants before production.
- Line 6: Rename sheet constants before production.
Deploy this example
- 01
Open Apps Script
In the bound spreadsheet: Extensions → Apps Script. For standalone projects, create one at script.google.com and link your Sheet by ID.
- 02
Paste and save
Add a .gs file, paste the code below, rename constants at the top (sheet names, column letters, API property keys), then save.
- 03
Authorize once
Run the main function from the editor. Accept OAuth scopes when prompted — triggers cannot run until authorization succeeds once.
- 04
Add the trigger
Triggers → Add trigger → choose the handler function and event (time-driven, on edit, or on form submit). Delete test triggers before production.
Before you run: build spc x-bar and r chart data
- 1Setup tabs exist with headers matching buildSpcControlData
- 2Dry-run on a copy workbook
- 3Timezone verified
- 4SpreadsheetApp authorization completed
- 5Output spot-checked against hand calc
- 6Time-driven trigger added only after validation
- 7Owners + alert recipients documented
Frequently asked questions
At minimum the tabs listed in the setup table for Build SPC X-bar and R Chart Data. Output tabs may be cleared each run—do not store source-of-truth data there.
Run from the Apps Script editor for dry runs. Production usually uses a Time-driven trigger after OAuth succeeds once.
Trailing points that do not fill a full subgroup of 5 are dropped until more data arrives.
Per-cell calls burn quota and wall time. One read + one write keeps this pattern under the 6-minute execution cap longer.
PropertiesService (Script Properties) for API keys and alert inboxes. Config sheet is fine for non-secret thresholds.
Simple ratios maybe; build spc x-bar and r chart data needs joins, branching, or side effects (email/Docs/API) that Apps Script handles cleanly.
Keep the .gs in clasp/git. Avoid divergent copies of formulas on the output tab—regenerate from the script.