Control-Chart Limits

Control-Chart Limits define, per method and element, the expected value and control limits of the laboratory's own control material (ISO/IEC 17025 §7.7.1). This is a Shewhart chart: it judges whether the measurement process is in statistical control.

It is not a customer conformity specification. That is the job of Acceptance Criteria (§7.8.6), and the distinction matters: changing a limit here never changes a ✓ or ✗ on a customer report.

Found under: Quality Control → Control-Chart Limits.

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Record Actions

Clicking the icon on each row shows:

Edit — Open the edit form
Delete — Delete the record (with confirmation)

Fields

Field	Description
Document No.	Leave blank for automatic numbering; can only be set at creation
Laboratory Method	Which method — required
Element	Which element — required
Expected Value	The centre line of the chart
Lower / Upper Limit	The control limits
Uncertainty	The uncertainty of the control material
Replicate RPD limit %	The replicate agreement limit (§7.7.1f)
Notes	Additional remarks

Where they are used

When you record a result on a Control Sample and pick an element, the system finds the limit for that method and element pair and fills in the expected value and limits automatically. If no limit exists, it warns you.

Connects to

Points at — this page does not stand without these:

If this is missing

🔴 Until a control series is locked, the limits here are the only §7.7.1 gate the QC result

has. With no limit for the method-element pair, an out-of-range control sample is **judged by

nothing** for the whole warm-up life of that series.

The rpdLimit judges original-versus-replicate agreement (§7.7.1(f)). Missing here, the system

falls back to the Settings default. **Missing there too, the element is reported with

pass = null** — informational only, with no judgement and no message saying so.

These are process limits, not a statement of conformity. Do not confuse them with Acceptance

Criteria: those judge the customer's result, these judge whether the method is in statistical

control.

Notes

One limit per method and element. A second entry for the same pair is refused; update the existing one instead.
The values are entered, not computed by this page. The limits come from your own control data and you record them here.
🔴 A blank RPD limit does not mean "no check". It falls back to the default in Settings; only if that is blank too is nothing checked.
Westgard rules are not configured here — they are applied on Control Samples and Control Series.
The row action menu prints a single-limit sheet with a signature block.