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Performance versus prescriptive specifications · Lesson 3 of 4

Performance versus prescriptive specifications: methods and worked application

A five-part method for writing a performance requirement, reading published ratings against a required pressure, working joint spacing from a prescriptive limit, and finding the flatness minimum for a face.

You will be able to: Turn a need into a performance requirement with a result, criterion, test method, evidence and verifier, and work three checks with every input labelled as data or assumed.

10 min · 11 slides · 7 questions

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Slide 1 of 11

Turn a need into a performance requirement

A performance requirement needs five parts: the result, a criterion with a unit, a named test method, the evidence to submit, and who verifies it.

That five-part check is a teaching method for this course, not a quotation from a standard.

From a need to an enforceable requirementSeven boxes in a column joined by arrows: need, result stated, criterion with a unit, test method named, evidence required, who verifies, accept or reject. A side box on the test method step says that with no test method named the clause cannot be enforced.Writing a performance requirementNeedResult statedCriterion with a unitTest method namedEvidence requiredWho verifiesAccept or rejectNo testmethodnamed:cannot beenforced

Seven boxes in a column joined by arrows: need, result stated, criterion with a unit, test method named, evidence required, who verifies, accept or reject. A side box on the test method step says that with no test method named the clause cannot be enforced.

The five parts of a performance requirement, in order. This is a teaching method for this course, not an AFS procedure or a quotation from a standard.

Sources

Glossary

Sustained pressure
The ES-1 test value Drexel Metals publishes for a system; Drexel states that the design engineer must apply the factor of safety.
Factor of safety
A multiplier the engineer of record applies to a required design pressure before comparing it with a tested value; ES-1 itself sets none.
Basis of design
A specification approach that names one product as the standard of comparison while allowing others that meet its stated characteristics.
Evidence missing
AFS Spec Match's status for a performance criterion that has no test evidence on file for the exact assembly.