Uncertainty Evaluation Form 20211207.docx Page 1 of 3

Uncertainty Evaluation Form

NOTES: SOP expected to be NIST OWM publications that include published uncertainty budget tables and may 

include alternative publications that include technically validated uncertainty budget tables. Numbers in 

parenthesis correspond to ISO/IEC 17025:2017.

Uncertainty Step 

and Factors from 

SOP 29

Evaluation and Verification Notes

List Reviewed 

Objective Evidence,

Note Action Items

Laboratory 

uncertainty 

documents

- Excel file includes good document control and records of reviews 

and changes (authorized changes, evaluations, approvals and dates)

(8.3.2) 

- Includes records of Software V&V. See GLP 15, Form A / Appendix A

- Filenames include dates and/or good date references in the files to 

indicate updates and reviews (“Electronic File Organization Tips”)

- GUM and SOP adoptions are current, correct, and complete with 

titles and dates (7.2.1.2, 7.2.1.3)

- Consistent approaches are used throughout the Scope with good 

software design and data management concepts, especially 

regarding document control, linking of date, and use of updated 

components (7.11)

3.1 Measurement 

equation (Specify)

- SOP includes equations that can be used in uncertainty evaluations 

(7.2.2.1) – also for lab developed procedures; what are the revision 

dates and selected options (and are they identified in the 

spreadsheet)

- Each component in equation includes evidence of traceability and 

uncertainty (6.5.1)

- Standards used have certificates and uncertainties are up to date in 

the Excel file (internal calibrations) (7.6.2)

3.2 Uncertainty 

components 

identified

(Identify) 

- Identifies and uses appropriate analysis for each component (7.6.1)

- List is complete and calculations include all components based on 

SOP used (complies with SOP)

- Items considered negligible must be documented and valid

- Components are clearly identified (labeled, not just with variables); 

longer heading names, list at bottom or comments added below 

tables to clarify

- Includes up to date repeatability from control charts or repeatability 

data 

- Reproducibility is reflected with check standards or suitable 

alternative approaches (identify how if no check standards)

- Includes uncertainties for standards that are correct/current and 

with verifiable certificates 
Uncertainty Evaluation Form 20211207.docx Page 2 of 3

Uncertainty Step 

and Factors from 

SOP 29

Evaluation and Verification Notes

List Reviewed 

Objective Evidence,

Note Action Items

3.3, 3.4 

Components 

quantified 

correctly 

(Quantify and 

Convert)

- Component values represent “1 sigma values” (using correct 

divisors for distributions where appropriate; distributions are 

identified in laboratory documents)

- Units are correctly represented (e.g., not inappropriately combining 

mass and temperature units in an uncertainty calculation)

- Values are all CURRENT – representing latest calibrations and 

current control chart values

- May use baseline approach, partial derivatives, or Kragten approach 

to identify individual component contributions 

3.5 Calculate the 

Combined 

Uncertainty

(Combine)

- All values represent the same units and are 1 sigma before 

combined (e.g., mass for mass, not °C in a mass RSS)

- Calculated correctly as root sum square (unless alternative 

equations are used for unique measurements that must be 

identified)

3.6 Expand 

combined 

uncertainty with 

appropriate k

value (Expand)

- Control chart data or repeatability data includes suitable degrees of 

freedom based on statistical procedures (> 25 for confidence in 

uncertainties); action items identified for low degrees of freedom

(minimum 7 to 12 required to start charts and larger k values used

as needed); (evaluate control charts and note gaps in Excel file for 

Unc)

- Coverage factor, k value is based on degrees of freedom OR 

- Includes Welch-Satterthwaite equation to calculate effective d.f.

and not just d.f. in control charts (evidence)

3.7 Evaluate 

Uncertainty 

(Evaluate)

- Pn assessments (suitability and compliance with decision rules)

o Tolerances listed are verified as current; tolerance source 

document is listed with revision date

o Correct decision rules are used, and calculations are correct

o Pn failures have associated action items and are not being 

performed for current calibrations (it’s nonconforming work 

to do with failures!)

- Represents the realistic uncertainty of measurements for submitted 

standards (7.5.1 and SOPs use “duplication of the process”)

- Meets customer requirements and expectations (decision rules 

documented in contract reviews with customers?)

- Expanded uncertainty values are NOT less than published scope

(NVLAP) or submitted values (OWM) without updating and 

submitting to Recognition or Accreditation bodies
Uncertainty Evaluation Form 20211207.docx Page 3 of 3

Uncertainty Step 

and Factors from 

SOP 29

Evaluation and Verification Notes

List Reviewed 

Objective Evidence,

Note Action Items

3.8 Report

(Report)

- Values of units match measurement results on certificates (7.8.4.1 

a); there are exceptions in mass where conventional mass 

corrections can be reported in mg units (even for avoirdupois

standards)

- Reported values are rounded correctly in Uncertainty files and on 

certificates (no more than 2 significant digits)

- Calibration certificates include: a complete Uncertainty Statement 

that includes method of combining components; list of components 

included and components that are not included; k factor(s) used; 

and statement that confidence levels reported to approximately 

95 %

- Statement includes GUM compliance (SOP 29 compliance) with full 

title and revision date

- May include decision rules reference or statement regarding how 

uncertainties are used in decisions regarding conformity – could be 

included in conformity statement.

- NVLAP requirement: “Uncertainty was taken into account when 

determining conformity”.

Other 

Observations

Uncertainties use an estimation process to quantify a value to be 

associated with reported measurement results. Use of statistical 

methods (Type A) are estimates of repeatability. Values are reported to 

approximately a 95 % level of confidence, which is also a statistical 

estimate.