What this is
What is a statistical process control log?
What is a statistical process control log?
It is the record made at the point of measurement: the reading, the time it was taken, whether it falls inside the control limits, and whether the accumulating points show a pattern. It is a per-event record, not a periodic report, and its value depends on being completed at the time, by the person running the process.
Who completes the log?
The operator running the line, at the interval set for the characteristic. The log is only useful as a control if the person closest to the process is the one plotting it, because a delay between the reading and the plot removes the chance to react before more product is made against a shifted process.
How does the log differ from the chart review?
The log is the raw capture: one row per reading, checked against the limits and the run rules as it is entered. The chart review is a separate, periodic instrument that looks back across the accumulated log to judge whether the limits are still valid, whether the chart is being used as intended, and whether the process is capable, not merely in control on any one day.
Scope
When is a statistical process control log required?
The log is the per-reading instrument in the statistical process control programme. Using it to do the work of the chart it feeds, or the plan that set its limits, produces a record nobody can report from later.
Use this template when
- A characteristic on the control plan is due its scheduled subgroup reading
- A new lot, batch or shift starts and the characteristic needs a fresh run of readings
- An operator observes a reading that may be outside limits and needs to record the check and the response
- The line is running and the log is the mechanism by which drift is meant to be caught before failure
- A linked record needs this one to exist: the control plan or the asset it is tied to
Do not use it for
- Control Plan, which sets the characteristic, the method, the frequency and the reaction plan the log then executes against
- Statistical Process Control Chart Review, which looks back periodically across the accumulated log to judge limit validity and process capability, rather than logging a single reading
- Process Capability Study, which uses a stable run of data to establish whether the process can hold the specification at all
- Setup Approval Record, which confirms a new or changed setup is correct before routine logging resumes
- Maintenance Calibration Record, which establishes whether the gauge producing the reading can be trusted in the first place
Compliance mapping
Which ISO 7870 requirements does this satisfy?
SPC logging is method-driven rather than statute-driven: ISO 7870 sets out how a control chart and its limits are constructed and read, and quality and food-safety management standards require that the monitoring it produces feeds corrective action and process evidence.
| Clause | Requirement | Where it lands |
|---|---|---|
| ISO 7870-2 | Shewhart control limits calculated from process data, not from specification, and applied consistently to the plotted characteristic | Header |
| ISO 7870-1 | General guidelines for using control charts to control a process at the point of production | Readings |
| ISO 7870-2 | Run-rule interpretation of accumulating points, including runs on one side of the mean and sustained trends, as evidence of a process shift | Pattern checks |
| ISO 9001 cl.9.1.1 | Monitoring and measurement of process performance, with methods determined and results retained | Response |
| ISO 9001 cl.10.2 | Reaction to nonconformity, including evaluation of the need for action to eliminate the cause | Response |
| Codex Alimentarius HACCP Principle 4 | Establish monitoring procedures for critical control points, recorded at the frequency the plan specifies | Readings |
| ISO 22000 cl.8.5.4 | Monitoring of critical control points with corrective action taken on deviation | Response |
What it does not cover
- Control Plan, which fixes what is measured, how often, by what method and what to do at the limit, and which the log only executes against.
- Process Capability Study, which establishes whether the process can hold the specification at all, using a stable run of data rather than an ongoing log.
- Statistical Process Control Chart Review, which is the periodic, look-back judgement of whether the accumulated chart's limits and usage are still sound.
- Maintenance Calibration Record, which is what establishes whether the measured value can be trusted at all.
- Gage R&R Study, which quantifies how much of the variation the log records actually comes from the measurement system rather than the process.
Global
Statistical Process Control Log requirements by country
The obligation to hold a process in statistical control is rarely a direct statute; it arrives through the quality or food-safety management system a site has adopted, and through the customer or auditor who expects the chart to be real.
21 CFR 820.250 (Quality System Regulation, statistical techniques)
Where statistical methods are used to control or accept product, the methods must be established and documented, and sampling plans must be based on a valid statistical rationale.
An FDA-regulated site cannot treat the log as informal housekeeping; the methodology behind the limits and the response has to be defensible on inspection.
BRCGS Global Standard for Food Safety, process control clauses
Sites certified to BRCGS must demonstrate monitoring of critical process parameters with records that show deviations were identified and corrected.
An auditor will ask for the log entries around a known deviation and expect the response section, not just the reading, to be complete.
ISO 7870 series; Codex Alimentarius HACCP Principle 4
ISO 7870 sets the method for constructing and reading the chart; Codex sets the requirement to monitor critical control points at a defined frequency.
Neither instrument mandates this specific form, but both require that whatever form is used produces a real, timely, actionable record.
How to complete it
How to complete a statistical process control log, step by step
The log's fields prompt for a reading and a check. Whether the record is defensible afterwards depends on judgement calls the fields do not make for the operator.
A reading inside the control limits still has to be read against the run rules: seven points on one side of the mean, seven trending, or another unusual pattern. Logging only the point-outside-limits check and leaving the pattern fields as a formality misses the earlier and more common signal.
Subgroup size and the method of forming it change what the plotted point represents. A log that varies the subgroup informally, sometimes one piece, sometimes five, without recording it, produces a chart that looks continuous but is not measuring the same thing from row to row.
An out-of-control signal can be logged the moment it appears; the special cause behind it is often not known yet. Recording 'suspected' honestly, with the reasoning, is more useful later than a special cause guessed at speed and left uncorrected in the record.
A capability study or CAPA that the signal warranted has to be started from this record, with its reference entered back into the log. A signal logged as present with no onward reference is a chart that noticed the problem and then did nothing with the notice.
What auditors find
Most common statistical process control log findings
The log almost always exists and is almost always populated at the point-outside-limits question. The findings concern the fields around it.
| Finding | Clause | What fixes it |
|---|---|---|
| Reading logged as within specification with the control-limit and pattern checks left blank or defaulted. | ISO 7870-1 | Require the control-limit and pattern fields on every subgroup, independent of the specification result. |
| Pattern checks answered 'No' by default without the accumulating points actually being reviewed against the run rules. | ISO 7870-2 | Train operators on the run rules with worked chart examples, and spot-check pattern answers against the plotted data. |
| Out-of-control signal logged with no action taken and no reason recorded for why none was needed. | ISO 9001 cl.10.2 | Make the action-taken field mandatory whenever a signal is present, accepting a documented 'no action needed' rather than a blank. |
| Control limits entered once and never distinguished from the specification limits on the same row. | ISO 7870-2 | Carry control limits from the control plan or the last valid chart review rather than re-entering them from the specification. |
| Subgroup size not recorded, or varying between entries without explanation. | ISO 7870-1 | Fix the subgroup size and method in the control plan and require the log to match it or flag the deviation. |
| Deviation case or capability study referenced as triggered but the linked record does not exist. | ISO 22000 cl.8.5.4 | Do not allow the log to close as 'triggered' without a resolvable reference to the record it should have raised. |
Case in point
Case in point: the chart that agreed with itself
A dairy line logged fill weight on cultured milk cartons three times a shift. For six weeks every reading landed inside specification, and the log's point-outside-limits answer was 'No' every time, so the operator stopped checking the pattern fields and began entering 'No' there too, without reading the chart. The process had in fact drifted upward across those six weeks, a run visible in hindsight as seven, then eleven, consecutive points above the centre line.
The drift was only caught when a downstream yield report showed product cost creeping up on a line that had reported nothing wrong. The subsequent review found every pattern-check answer for six weeks had been entered without the operator plotting or reading the run, because the specification test alone had never failed and the pattern fields had come to feel redundant. The fix was not a new field; it was making the pattern check a genuine read of the chart at the point of entry, verified by spot audit, rather than a box answered from the specification result.
The template
The template, field by field
The form exactly as it installs. Every field, option, score and conditional rule is editable, and the links to other templates come with it.
4 sections
- Reference
- QUA-058
- Archetype
- Log
- Record ID
- SPC-2026-000
- Scoring
- Capability index
- Direction
- High is good
- Singleton
- No
- Basis
- ISO 7870
- Links
- Links Control Plan, Asset
- Tags
- Process, Analysis
- Sections
- 4
- Fields
- 45
- Follow up fields
- 7
- Repeating sections
- 1
- Links out
- 4
Header
19 fieldsLog ID*
Auto sequence. Format SPC-2026-0000.
The record's own ID. Other templates point at this value.
Status*
Drives who this goes to next.
- Planned2 pts
- In progress2 pts
- Complete3 pts
- Deferred0 pts
- Open0 pts
- Closed3 pts
- Overdue0 pts
Date and Time*
Raised By*
Site*
Site ID*
Format SITE-000.
Links to FDN-001 Site ID
Line*
Shift*
Line Lead
Batch Number*
Numeric key joining to your ERP batch record.
Links to External system reference
Product*
Production Date*
Control Plan Reference
Links to QUA-057 Plan ID
Characteristic*
Chart Type*
Individuals and moving range, X bar and R, p chart or c chart.
Upper Control Limit
Lower Control Limit
Specification Limits
Control Limits Are Not Specification Limits
Control limits describe what the process does. Specification limits describe what the customer needs. A process can be in control and still make bad product.
Readings
Repeats6 fieldsReading Time*
Subgroup Size
Measured Value*
Within Control Limits*
- Yes3 pts
- No0 pts
Within Specification*
- Yes3 pts
- Borderline1 pt
- No0 pts
Recorded By*
Pattern checks
6 fieldsLook For Patterns, Not Just Breaches
A run of seven points on one side of the mean, or seven rising, means the process has shifted even though nothing is out of limits yet. That is the point of charting.
Point Outside Control Limits*
- No3 pts
- Yes0 pts
Seven Points One Side Of Mean*
- No3 pts
- Yes0 pts
Seven Points Trending*
- No3 pts
- Yes0 pts
Unusual Variation Pattern*
- No3 pts
- Yes0 pts
Process In Statistical Control*
- Yes3 pts
- Marginal1 pt
- No0 pts
Response
14 fieldsOut Of Control Signal Present*
Repeats the control assessment so the response steps sit in this section.
- No3 pts
- Yes0 pts
Out Of Control Action Taken
Special Cause Identified
- Yes3 pts
- Suspected1 pt
- No0 pts
Deviation Case ID
Thread key
Capability Study Triggered
Study ID
Links to QUA-059 Study ID
Action Required*
Raise the action record, then enter its reference here.
- No2 pts
- Yes0 pts
Priority
- High0 pts
- Medium1 pt
- Low3 pts
CAPA ID
Format CAPA-2026-00000.
Links to FDN-014 CAPA ID
Action Owner
Line Lead*
Signature*
Quality*
Second Signature*
QUA-058 · record IDs look like SPC-2026-000 · Links Control Plan, Asset
Open in KnowellaRun it with agents
From a document you fill in to a programme that runs itself
The log is easy to fill in and easy to fill in on autopilot. What actually slips is the pattern read, the timely response, and the link forward to the record a signal should have raised.
Holds the log against the control plan's stated frequency and limits, flags subgroups logged late or with inconsistent sizing, and checks that a signal has a resolvable reference forward.
Watches for pattern-check answers that stop varying across a run of entries and surfaces that as a likely autopilot signal before it reaches a chart review.
Ties the gauge behind each reading to its calibration status, so a drifting chart can be checked against the measurement system before it is read as process drift.
This template lives in KnowQuality — quality and food safety. HACCP, nonconformance, traceability, laboratory and customer complaints.
Meet KnowQuality→Glossary
Statistical Process Control Log definitions and key terms
- Control limit
- The boundary calculated from the process's own historical variation, describing what the process actually does, as distinct from what the customer will accept.
- Specification limit
- The boundary set by the customer or design requirement, against which a unit is judged acceptable or not, independent of the process's own behaviour.
- Subgroup
- The set of readings taken together and treated as one point on the chart; its size and method of formation must stay consistent for the chart to remain meaningful.
- Special cause
- A source of variation outside the process's usual behaviour, identifiable and often correctable, as distinct from the common-cause variation always present.
- Run rule
- A pattern test, such as seven consecutive points on one side of the mean or seven trending in one direction, that flags a process shift before any point breaches a control limit.
FAQ
Frequently asked questions about statistical process control log
Why log a reading that is inside specification?+
Because the specification test and the control test answer different questions. A reading inside specification can still sit outside the control limits or form part of a run, both of which indicate the process has shifted, and the shift will eventually produce a failed reading if it is not acted on now.
What counts as an out-of-control signal?+
A point outside the control limits is the clearest case, but the pattern tests matter as much: seven points running on one side of the mean, seven trending in a direction, or another recognised unusual pattern. Any of these means the process has changed even though no single reading has breached a limit.
Should the operator or quality raise the resulting action?+
The operator raises the signal at the time it is seen, because delay defeats the purpose of logging in real time. Quality typically owns the CAPA or capability study that follows, but the log's reference to it should be entered as soon as the record is raised, not left open.
How is this different from the chart review?+
The log is the raw, per-reading record made continuously by the operator. The chart review is a separate periodic instrument, carried out by quality engineering, that looks back across the accumulated log to check whether the limits are still valid and the process is capable, not just whether any one reading was in control.
What if the special cause can't be identified?+
Record 'suspected' with the reasoning rather than closing the signal against an unverified cause. A signal closed on a guessed cause that turns out wrong leaves the actual cause unaddressed and free to recur.
Does a capability study replace the log?+
No. The capability study answers a different question, whether the process can hold the specification over a stable run, and it depends on the log's data to have that run in the first place. Neither instrument substitutes for the other.
Keep going
Related templates and programmes
Industries this is written for
Programmes this belongs to
Used together in HACCP and Food Safety
Unannounced Audit Readiness Check
Checks whether the site would pass an audit arriving today, covering records, standards and area condition
Product Nonconformance Report
Records product that does not meet specification
Hold and Release Record
Places suspect product on hold and records the decision to release, rework or scrap it
HACCP Plan
The hazard analysis and critical control point plan for a product or process
HACCP Verification Record
Confirms the HACCP plan is being followed and still works
CCP Monitoring Log
Records readings at a critical control point, such as cook temperature, chill time or metal detection
More in Process Control
Control Plan
Sets out what is measured on a process, how often, by what method and what to do when it goes out of limits
Process Capability Study
Measures whether a process can reliably hold its specification, using data from a stable run
Setup Approval Record
Confirms a new setup is correct and approved before the run continues past the first pieces
Batch Record
Records everything that happened during the production of one batch, including materials, settings, checks and people
Yield Analysis Record
Compares material in against product out and accounts for the difference
Shift Handover Record
Passes on what the incoming shift needs to know, including running issues, holds and changes
Written and reviewed by
Siddarth Singh
Founder & Chief Executive Officer, Knowella
Certified Safety Professional and industrial and systems engineer with more than a decade inside food supply chain, freight and manufacturing operations. This page was written against the current text of the standards it cites, not against secondary summaries of them.
- Certified Safety Professional (CSP), Board of Certified Safety Professionals
- MBA, University of Chicago Booth School of Business
- MS and BS, The Ohio State University, Industrial and Systems Engineering
- Six Sigma Black Belt
Sources and last review. Reviewed 16 August 2026 against:
- ISO 7870-1, Control charts — General guidelines
- ISO 7870-2, Control charts — Shewhart control charts
- ISO 9001:2015 clauses 9.1.1 and 10.2
- Codex Alimentarius, HACCP Principle 4 (establish monitoring procedures)
- 21 CFR 820.250, Quality System Regulation, statistical techniques
This page is general guidance, not legal advice. Confirm requirements with your jurisdiction’s regulator.