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Maintainability

KISS Principle

Simple enough to be repaired under bad conditions.

The article

If

"Keep it simple, stupid" came out of aircraft design, where the requirement was that a jet be repairable by an average mechanic in a field with basic tools. The test was never elegance — it was whether an ordinary person could fix it in the worst circumstances the thing would actually meet.

Then

Judge a design by who can repair it at 3 AM, not by how it reads in review. If the on-call engineer needs the author on the call, it is not simple — it is familiar to one person.

Unless

Ashby's Law of Requisite Varietya system simpler than the problem it has to regulate cannot cope with it, and simplicity below that floor is displaced complexity rather than less of it

Source

Attributed to Kelly Johnson at Lockheed's Skunk Works (c. 1960), as a field-maintainability requirement for combat aircraft.

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See also