C.16:5.3.1 - Construct the measurement relation

1. Start with what is being measured and why. Specify the subject, Characteristic, conditions and required range of interpretation under §§5.1-5.2. Separate what is already known from values the proposed measurement must resolve.
2. Follow how the indication is produced. Describe the procedure connecting the subject to the indication. Recover the measurement principle, applicable calibration relation, or combination of both that connects the quantities. Include intermediate conversions when they change the answer. Physical laws, assessment models and instrument-specific relations come from the relevant subject knowledge; B.5:4.2 helps recover their construction.
3. Include influential conditions. Consider how the apparatus interacts with the subject, what it samples or averages, and its resolution and operating range. Include an influence when its omission could change the interpretation needed for this use. Explain a correction through the relation that gives its direction and magnitude. Retain an unknown influential quantity as unknown, using available bounds or distributions when justified.
4. Determine what the relation resolves. With actual or proposed indications, derive the compatible sought values and their uncertainty under §5.4. If different sought values can produce the same indication, identify that ambiguity. Work a small case or limiting case to expose an omitted influence, inconsistent units or a failed inversion. C.16.IR constructs the joint cases and distinguishes feasible alternatives from bounds that may include unattainable values.
5. Choose the useful return. Supply the interpreted value, interval or conditional result when it answers the question. Otherwise identify which change could resolve the remaining ambiguity: refine the relation, change the measurement arrangement, obtain an applicable calibration or narrow the conclusion. Choose further observation by the distinction it can resolve and the work it demands, using C.11.DUA when that choice needs deliberation. C.16.RM compares changes to models, arrangements and calculation, then carries the selected repair through the interpretation while retaining the wanted quantity.

When an observed discrepancy matters, compare its plausible sources in the subject account, measurement relation and actual arrangement. Change the contribution that can alter the answer; sometimes removing an unwanted influence from the arrangement is more useful than modeling it in greater detail. A model-development result states the relation and what it would establish. A claim about a performed measurement also identifies the work and obtained result under §§5.3-5.5.