ISKRIT / Metrology / QC · Shewhart charts
Metrology
Internal laboratory quality control and Shewhart control charts for accredited laboratories
Shewhart control charts with zones, both checked against the instability criteria, freezes limits from a baseline period, computes repeatability with outlier screening and an uncertainty budget. Built for internal laboratory quality control.
Data current as of 2026-09-26
Standards
Charts per ISO 8258, repeatability and trueness per ISO 5725 parts 2 and 6, coverage factor per the GUM. The chart factors A2, A3, B3, B4, D3, D4, d2 and c4 are the ISO 8258 table 2 values.
Input
Result series labelled with a control level, pairs of duplicate determinations, or control against a reference material.
Output
Charts with zones, verdict on the criteria, a level-by-level control summary, repeatability, uncertainty, report.
What it does
- Shewhart charts with zones, a verdict, repeatability and uncertainty
- Load series from Excel, export to XLSX, printable control report
- Methods and series are stored on the server and reopen next time
Price
Free in full, no sign-up and no payment.
Open the calculator →Questions
Are both charts checked?
Yes. The means chart against all eight criteria, the range chart against the out-of-limit rule, because zone criteria do not apply to the skewed distribution of the range.
Can limits be frozen from a baseline period?
Yes, limits are computed from the first N stable series and later points are checked against them.
Is repeatability calculated?
Yes, s_r iteratively with screening of pairs above the limit r = 2.77·s_r, with a verdict for each pair.
How is a method controlled at several concentrations?
Every series carries a control level. The chart, its limits, the baseline period, the σ_r requirement and the repeatability are computed for each level on its own, and a summary shows the verdict for all levels at once.
In the reference
- Measurement uncertainty calculator: GUM budget with Type A, Type B and expanded U
- Calibration intervals: setting them, shortening them, defending them
- Shewhart control chart constants: A2, A3, B3, B4, D3, D4, d2, c4
- The eight out of control tests on a Shewhart chart
- Repeatability and reproducibility limits: where 2.77 comes from
- Rebound hammer calibration: why the factory curve is not enough