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Showing 1681–1709 of 1709 reference entries

Measurement · PhysicsRadiant flux, intensity, irradiance, exitance and radiance

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

DefinitionMeasurement · PhysicsPhotometric weighting, lumen, candela, lux and luminance

Photometry weights radiation with a specified standard visual response.

DefinitionMeasurementWriting SI quantities and unit symbols

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

DefinitionMeasurementGram prefixes and the kilogram exception

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

DefinitionMeasurementRounding a result with its uncertainty

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

MethodMeasurement · Physics · ChemistryCommon non-SI units and exact SI conversions

Common non-SI unit names require their correct SI scale factors.

DefinitionPhysics · ChemistryGas pressure as molecular momentum transfer

Molecular collisions link macroscopic pressure to random translational motion.

ModelChemistry · PhysicsOrdinary aggregate states and bulk behavior

Solid, liquid and gas describe bulk behavior rather than chemical identity.

ModelChemistryInferring empirical and molecular formulas from composition

Element mass ratios become atom ratios through molar masses, with uncertainty and sample identity retained.

MethodChemistryLewis structures and valence-electron accounting

A Lewis diagram accounts for bonding and nonbonding valence electrons in a specified connectivity.

MethodChemistryElectron-domain geometry and molecular shape

VSEPR distinguishes the arrangement of electron regions from the positions of atoms.

ModelChemistryElectronegativity, bond polarity and molecular polarity

Polar bonds can cancel in a molecule; molecular geometry matters.

ModelChemistrySolutions, solutes, solvents and solvation

Dissolution disperses specified molecular or ionic species in a solvent.

DefinitionChemistrySolubility, saturation and supersaturation

A saturation limit is an equilibrium property under specified conditions, not a synonym for concentration.

DefinitionChemistryFiltration separates retained solids from a fluid

Ordinary filtration separates undissolved particles; dissolved species can remain in the filtrate.

MethodChemistryDistillation and vapor–liquid composition

Distillation uses vapor–liquid partitioning and condensation, with a limit at an azeotrope.

MethodBiologyGene, allele, genotype and phenotype

Genomic sequence variants and observable traits describe different levels of biological information.

DefinitionBiology · ChemistryEnzyme substrates, active sites and induced fit

Substrate recognition and catalysis depend on a dynamic molecular environment.

ModelBiology · ChemistryMonomers, polymers and hydrolysis

Covalent subunit linkage and water-assisted cleavage explain biological polymer structure.

DefinitionBiology · ChemistrySugars, glycosidic linkages and polysaccharides

Sugar connectivity distinguishes energy-storage and structural polysaccharides.

DefinitionBiology · ChemistryFatty acids, storage lipids and membrane lipids

Lipids include several architectures rather than one repeating-monomer polymer class.

DefinitionBiology · ChemistryAmino-acid residues and peptide linkages

The peptide backbone and variable side chains are different parts of protein structure.

DefinitionBiology · ChemistryNucleotides and DNA/RNA backbone polarity

Bases carry sequence information on a chemically directional sugar–phosphate backbone.

DefinitionBiologyCell membrane, cell wall, cytosol and compartments

A cell's boundary, fluid interior and specialized structures have different roles.

DefinitionEarth & cosmos · MeasurementEarthquake location, source magnitude and local intensity

A source location or magnitude does not describe the shaking experienced at every site.

DefinitionEarth & cosmosAtmospheric composition and thermal layers

Composition and temperature structure describe different features of Earth's atmosphere.

ModelEarth & cosmosDrainage basins, outlets and water divides

Surface drainage boundaries depend on the chosen outlet and need not bound groundwater flow.

DefinitionEarth & cosmosThe celestial sphere and the observer's sky

A sky direction is an angular observation, not an object's three-dimensional distance.

ModelEarth & cosmos · MeasurementRight ascension, declination and reference epochs

Celestial angular coordinates require a declared reference system and date conventions.

Definition
MethodSource checked

Rounding a result with its uncertainty

Measurement

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

Key knowledge

Retain guard digits during uncertainty calculations, then report the estimate and uncertainty with consistent decimal places. The GUM usually recommends at most two significant digits for standard or expanded uncertainty, with more digits when needed to avoid consequential rounding error. For example, y=12.34567 m with u(y)=0.023 m can be reported as y=12.346 m and u(y)=0.023 m.

Values and equations

y=12.34567 m, u(y)=0.023 m → reported y=12.346 m, u(y)=0.023 m

y
Measured estimate in the worked rounding example m
u(y)
Standard uncertainty of that estimate m

Conditions and scope

  • The example reports a standard uncertainty, not a confidence interval or guaranteed error bound.
  • The two-digit rule is guidance rather than a universal requirement; preserve justified extra digits for subsequent calculations or applicable reporting rules.
  • A reported digit count alone does not establish accuracy, calibration or traceability.
Sources · 3

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Evaluation of measurement data — Guide to the expression of uncertainty in measurement, JCGM 100:2008Joint Committee for Guides in MetrologyReference guide · PDFbipm.orgRead source
  2. National Physical Laboratory (NPL)2 sources
    1. A Beginner’s Guide to Uncertainty of Measurement · GPG11, Issue2Stephanie Bell · NPLReference guide · PDFnpl.co.ukRead source
    2. Uncertainty Evaluation · NPL Report MS6M. G. Cox and P. M. Harris · NPLReference guide · PDFeprintspublications.npl.co.ukRead source

Evidence and review

Reported estimates are rounded consistently with stated uncertainty while retaining calculation guard digits to avoid round-off error.

2026-10-10 · Independent Chemistry, Biology and Earth/Cosmos editor (AI editorial review). Source checks and independent AI editorial review of compact reference claims, equations, units, conditions and conceptual mappings. This is not human specialist certification, laboratory accreditation, whole-book verification, or a claim that all possible foundational knowledge is present.

Foundational review

2026-10-10 · Independent AI editorial inspection of this new compact reference entry, its equations, applicability, sources and knowledge connections.

Sources from other places

Scope or convention differs

Guard digits and final rounding avoid false precision; estimate decimal places should reflect the stated uncertainty.

The beginner guide always rounds uncertainty upward; the repository keeps this as a contextual choice and distinguishes standard uncertainty from a coverage interval.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–2 of 2 relationships

Scientific relationships · 2 / 2

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 1

    Linked statements

    • Retain guard digits during uncertainty calculations, then report the estimate and uncertainty with consistent decimal places. The GUM usually recommends at most two significant digits for standard or expanded uncertainty, with more digits when needed to avoid consequential rounding error. For example, y=12.34567 m with u(y)=0.023 m can be reported as y=12.346 m and u(y)=0.023 m.

    Consistent digits supplement the existing requirement to state the model, units, conditions and uncertainty interpretation.

  2. Related to
    Relationship sources · 1

    Linked statements

    • Retain guard digits during uncertainty calculations, then report the estimate and uncertainty with consistent decimal places. The GUM usually recommends at most two significant digits for standard or expanded uncertainty, with more digits when needed to avoid consequential rounding error. For example, y=12.34567 m with u(y)=0.023 m can be reported as y=12.346 m and u(y)=0.023 m.

    The rounding guidance can also apply to expanded uncertainty, whose coverage factor and interpretation must still be specified.

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foundation-measurement-reporting-digits
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