Specification Development – part 3, Specification

FINALLY, we are able to execute the preparation of the specification proper. However prior to do so we need to be clear on whether we wish to prepare a “Descriptive/Function” or a “Prescriptive” specification.  Prescriptive specifications, where the specification defines ‘step-by-step’ the procedures to be followed, were the norm in the past and in some instances are the best choice. The trend however is towards the use of Descriptive or Functional specifications in which the document explains what desired result without describing the actual procedure to do so. Functional specifications are generally clear, achievable, measurable and enforceable.


Of course in actuality most final documents are a combination of the two techniques, using in some parts clear definitions of the metallurgy, dimensions, displacement or tolerances while leaving some discretion as to fill fluid or similar provided it meets or exceeds a certain temperature range.

Finally, the most important and often most difficult part of preparing specifications is bringing all the experts in the room to consensus on the best way to design the resulting product while also not limiting development of new ideas nor excluding a specific manufacturer or technology.

Fortunately, if the committee does not get it right the first time, specifications have a 5- year shelf life after which time they must either be ratified for an additional 5 years or revised to reflect the changes in the environment for which they were created.