Frequently Asked Questions (FAQs)

Frequently Asked Questions about Performance Specifications are listed below.

Performance Specifications

Q: What is a performance spec?
A: A performance specification states requirements in terms of the required results with criteria for verifying compliance, but without stating the methods for achieving the required results. A performance specification defines the functional requirements for the item, the environment in which it must operate, and interface and interchangeability characteristics.

Q: What guidance have we given on how to write a performance specification?
A: Writing performance specifications is not a new concept. We have been teaching how to write performance requirements for years at our specification training course. It has received extra emphasis in our training on how to write Commercial Item Descriptions. What is new is that we are now designating documents as "performance specifications." The following performance specification policy and guidance have been issued:
  • MIL-STD-961E(1) NOT 1, Defense and Program-Unique Specifications Format and Content, dated 10 March 2010.
  • Specific guidance on the development and use of performance specifications appears in the SD-15, Guide for Performance Specifications, dated 24 August 2009.

Q: Is it possible for a general specification to be designated as performance and its associated specification sheets to be designated as detail?
A: No. Since a general specification must be used together with a specification sheet, the fact that the specification sheet is detail requires the general specification also to be designated as detail.

Q: Within the same family of specification sheets, is it possible for some to be designated as detail and others to be performance?
A: Generally, no. The decision whether to convert a family of specification sheets to performance specifications must be consistent across-the-board. In some cases, however, the number of specification sheets that must be converted to performance specifications may be very large, making it difficult to convert all of them at one time. In this situation, there may be a temporary blend of detail and performance specification sheets within the same document number series. This situation is acceptable as long as the goal is to convert all of them to performance specifications.

Q: Can a performance spec ever cite a detail spec as a requirement?
A: The citing of a detail spec as a requirement does not automatically mean that a spec is not performance, but it is a strong indicator that as spec may not be performance. Performance specs should not cite any detail spec as a requirement if it demands a specific design solution. But performance specs may cite a detail spec if it relates to a physical or operational interface requirement. For example, it would be permissible to have a requirement in a performance engine specification that required the engine to operate with specific substances, such as lubricating oil or fuel, which conform to detail specs. The requirement that the engine be able to operate on a specific type of fuel is an operational interface requirement and does not dictate the specific design of the engine. It would not, however, be permissible in a performance spec to require that the engine be made of certain materials or that the various engine components conform to detail specs, since such requirements would dictate specific design solutions instead of stating the performance expected.