Friday, just before the shift change. Part of the plant fails. The technicians are on site quickly — and what begins is not fault-finding but a search for how things are actually wired. The drawings are incomplete, changes were added by hand over the years or not documented at all. The plant is down, the pressure rises, and nobody can rely on the sheet in their hand showing reality.
Documentation does not fall behind, it seeps away
Hardly any documentation goes out of date in one large step. It goes out of date in many small ones: a terminal added, a drive replaced, an address changed. Each individual change is too small to justify raising a job — and that is exactly why it is left undone. After two years there are fifty such small things, and the actual state can no longer be reconstructed from memory.
None of this ever shows in normal operation. It shows during a fault, when the documentation is genuinely needed for the first time in months.
And not only then. Periodic testing of electrical installations under DGUV Vorschrift 3, the German accident-insurance rule, assumes the person testing knows the intended state, and the German Ordinance on Industrial Safety (BetrSichV) requires a risk assessment for work equipment that rests on those same documents. A drawing set that no longer reflects the plant is therefore more than inconvenient.
What ongoing maintenance means in practice
The difference is not the care taken when incorporating a change — that is the same either way. It is whether there is a route for getting a change off your desk at all, without setting up a project for it.
In practice: the change is reported in whatever legible form suits — a photo of the red-pen markup, a note, a sketch. It is then incorporated properly into the CAE project, with a traceable revision status in the title block — the data fields that belong there are specified in ISO 7200. And the current state sits where somebody will find it during a fault, rather than in a mailbox.
The measure is not the page count
Documentation is not good when it is complete. It is good when a maintenance technician facing a fault can find what they are looking for without prior knowledge. That rests on two things: a state that reflects the plant, and a labelling system nobody has to decode first.
Neither is busywork for quiet days. It is preparation for the Friday afternoon when it matters.