A condition in which the acquisition customer provides contractual direction with regard to one or more design features in addition to those written into the development specification. Sometimes this happens because the customer wants to make best use of technical thoughts they’ve had; other times it happens because the System Engineering theoreticians try to avoid placing things into the specification that they think shouldn’t be there1; in other cases, it occurs because the use of some piece of equipment (or software) is the most certain means of managing some external interface.
No matter how it happens, this is a difficult circumstance, with many opportunities for failure along the way.
Footnotes- This is always the wrong answer. The customer has the prerogative to “require” any features that they see fit; putting it in the development specification and making them sign up to it is the very best way to assign responsibility (and, therefore, to indemnify the contractor).[↩]