Foundations

A complete measurement system can include more than one device.

Component names describe different measurement roles.

A displayed reading is only one part of a measurement result.

Changing an instrument response differs from determining its calibration.

An accepted comparison value need not be an exact true value.

Possible readings differ from a validated interval of measurement.

Instrument properties are specified within a domain of use.

Responding to a target differs from excluding interference.

An undetected input change differs from an interval with no output change.

Time stability differs from short-term repeatability.

A specification limit is not an uncertainty estimate.

More repetitions do not resolve an underspecified measurand.

Relative uncertainty uses a nonzero measured magnitude.

A zero or blank reading can still have uncertainty.

An intended-use target differs from achieved uncertainty.

Within-location changed conditions differ from strict repeatability.

Certification alone does not establish equivalence across procedures.

Relative atomic mass is dimensionless and depends on the isotope composition being averaged.

Molar mass converts a specified substance's amount into mass.

Concentration must declare its numerator and denominator.

A coordinate pair needs a reference surface, origin and convention.

Flattening Earth's curved reference surface requires a choice of distortions.

Height above a geometric reference is not automatically height above a gravity reference.

The astronomical unit and light-year measure lengths, with different defining conventions.

A solid angle measures a cone of directions rather than a plane rotation.

Optical power, directional power and surface densities are different quantities.

Photometry weights radiation with a specified standard visual response.

Symbol form, spacing and parentheses preserve the meaning of reported quantities.

Mass prefixes attach to gram even though kilogram is the SI base unit.

Report useful digits without treating extra digits as proof of accuracy.