I don't want ISO GPS! — But you have been using it all along
One inconspicuous symbol on the drawing — and the entire ISO GPS system applies. Many people in design, inspection planning and manufacturing believe ISO GPS is optional, or something for "high-end drawings" only. But as soon as even a single symbol from the ISO GPS universe appears — flatness, a datum, a surface texture callout — the whole set of rules applies.
Specifically: ISO 8015, clause 5.1
"Once a portion of the ISO GPS system is invoked in a product specification, the entire ISO GPS system is considered to be invoked unless indicated otherwise."
In other words: one GPS specification automatically invokes the whole system —
- the fundamental standards (ISO 8015, ISO 1101, ISO 5459),
- datum requirements (ISO 5459),
- the reference temperature (ISO 1),
- decision rules for conformity (ISO 14253).
Why this matters
It is binding. If you use ISO GPS in part, it applies in full — unless it is explicitly overridden ("per company standard XY"). Not knowing this risks misunderstandings in production, complaints, or legal problems in the conformity assessment.
A practical example
You specify a flatness tolerance —
You can find all symbols in our ISO GPS symbol overview.
With this one symbol the whole system takes effect:
- The tolerance zone is two-dimensional by definition.
- Measurement takes place at 20 °C (ISO 1).
- Measurement uncertainty has to be taken into account (ISO 14253).
Conclusion: say GPS and you say everything
Even "just a quick tolerance" opens the door to the entire ISO GPS house — and that is a good thing: it brings binding force, comparability and clarity. But only if you know the rules — for example from an ISO GPS workshop at your company.
Anyone using GPS symbols specifies far more than just a number. Anyone who does not want that has to say so explicitly. On the same theme: "The drawing is the law — what is not on it does not apply".
