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Institutional table from National Institute of Standards and Technology. Undated; cited magnesium-24, magnesium-25 and magnesium-26 neutral-mass and reference-composition rows.

Issued by National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

This source is credited to an organization.

Online text: physics.nist.gov/cgi-bin/cuu/Value?me%7Csearch_for=mass+of+electron

Cited passages: CODATA electron mass: numerical value and 2022 adjustment label.

By National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

This source is credited to an organization.

By National Institute of Standards and Technology. Handbook of Basic Atomic Spectroscopic Data, neutral helium He I table.

The table provides ground, singlet and triplet excitation energies as spectroscopic wavenumbers, and the He II ground-state ionization limit. Multiply by $hc$ with consistent inverse-length units to obtain excitation energy.

By National Institute of Standards and Technology. Handbook of Basic Atomic Spectroscopic Data, neutral oxygen O I table.

The first configuration block specifies $2s^{2}2p^4{}^3{P}_2$ as the zero-energy level, followed by its $J=1,0$ fine-structure partners.

By National Institute of Standards and Technology, CODATA.

Publisher: National Institute of Standards and Technology.

Online text: physics.nist.gov/cuu/Constants/Table/allascii.txt

Cited passages: 2022 CODATA complete listing: electron volt, elementary charge and Avogadro constant.

Cited passages: NIST's current constants table, 2022 CODATA adjustment: vacuum electric permittivity; NIST, 2022 CODATA complete table: Newtonian constant of gravitation and its standard uncertainty; NIST, 2022 CODATA constants; NIST, CODATA constants: Wien displacement law constants.

Cited passages: Current adjustment heading, next-adjustment notice and data-content update.

By National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

Online text: cccbdb.nist.gov/exp2x.asp?casno=7647010&charge=0

Cited passages: HCl, “Vibration specific dipole moments”: equilibrium 1.093 D and vibrational level 0, 1.109 D.

For a modern chosen example, the National Institute of Standards and Technology lists neutral magnesium atomic masses $23.985041697\mathrm{u}$, $24.985836976\mathrm{u}$, and $25.982592968\mathrm{u}$, with reference isotopic abundances $0.7899$, $0.1000$, and $0.1101$. They describe the isotopes with mass numbers 24, 25, and 26, respectively.^[ref] These modern inputs are not a reconstruction of historical observations.

Use the dimensionless mass-to-charge ratio coordinate $x=(m/\mathrm{u})/z$. For the illustration only, approximate ion masses by the neutral atomic masses. The singly charged positions are then near $23.98504$, $24.98584$, and $25.98259$; the doubly charged companions are near $11.99252$, $12.49292$, and $12.99130$. The neutral-to-ion correction already given above is essential at higher accuracy. A peak near $x=12$ alone need not identify a chemical element: another ion with a different electric charge can occupy the same mass-to-charge ratio interval.

For the narrow singly charged peak at $x\approx 24.98584$, the chosen full width at half maximum $\Delta x=0.12$ gives mass resolving power $R\approx 208.2$; widening to $\Delta x=1.20$ gives $R\approx 20.82$. Adjacent isotope spacings here are approximately one unit in $x$. Peaks are visibly separated in the first chosen profile and overlap strongly in the second. A small uncertainty in a fitted peak centre would not by itself make the overlapping components resolved.

Even integrated peak areas need a response model. For isotope fraction $f_i$, let ${\eta }_{i,z}$ collect the probability of ionization into electric charge state $z$, transmission through the analyzer, and the detection response. In a linear instrument with overall exposure factor $C$, the component area isEqual ${\eta }_{i,z}$ at a fixed $z$ makes normalized areas equal the fractions; otherwise it does not. In the chosen example, doubling only the mass-25 response changes the normalized areas to $0.71809$, $0.18182$, and $0.10009$, although the neutral sample is unchanged. Photographic darkening introduces another possible nonlinearity: neither line darkness nor peak height is a universal measure of neutral isotopic abundance. Calibration of position and calibration of intensity answer different questions. Matched standards, a known electric charge assignment, and a response correction make isotope analysis useful; a visually impressive set of peaks alone does not supply those controls.

Issued by National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

This source is credited to an organization.

Online text: www.nist.gov/pml/sensor-science/thermodynamic-metrology/mercury-thermometer-alternatives/mercury-thermometer-1

Cited passages: Platinum Resistance Thermometers, opening explanation: SPRTs as ITS-90 interpolation tools; Platinum Resistance Thermometers, opening explanation: conventional 100-ohm element at 0 °C.

Page created 14 December 2011; updated 16 April 2024. The creation timestamp is not an independently established first-publication date.

Issued by National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

Online text: www.nist.gov/pml/sensor-science/thermodynamic-metrology/mercury-thermometer-alternatives/mercury-thermometer-7

Cited passages: “Comparison with another calibrated thermometer at ambient temperature”, apparatus and steps 1–10; “Measurement at the steam point”, pressure and elevation correction.

Species entry in NIST Chemistry WebBook, SRD 69, published and hosted by the National Institute of Standards and Technology. No personal entry author is credited. The displayed 2026 copyright year is distinct from an entry publication or revision date.

Online text: webbook.nist.gov/cgi/cbook.cgi?ID=C877247

Cited passages: Formula C8H5KO4; Molecular weight 204.2212; CAS Registry Number 877-24-7; footer copyright.

Software reference manual issued and hosted by the National Institute of Standards and Technology. No personal whole-manual authorship or separate manual publication date is established. Individual entries distinguish webpage dates from implementation dates.

Official manual, Volume II: www.itl.nist.gov/div898/software/dataplot/refman2/homepage.htm

Entry in NIST Dataplot Reference Manual. The function name is PARPDF. Issued and hosted by the National Institute of Standards and Technology; no individual author is established from the contact address. The page gives both creation and last update as 23 August 2006; April 1994 is the function implementation date, not a publication date.

Official entry: www.itl.nist.gov/div898/software/dataplot/refman2/auxillar/parpdf.htm

Cited passages: Description, standard density and the tail-length and lower-bound parameters; footer, creation and update dates. The optional software location and scale arguments are separate from these two parameters.

Function RAYPDF in NIST Dataplot Reference Manual, issued by the National Institute of Standards and Technology; no individual byline is established. The page was created and last updated on 7 July 2004; June 2004 is the implementation date.

Official entry: itl.nist.gov/div898/software/dataplot/refman2/auxillar/raypdf.htm

Cited passages: Description, including the location and scale convention; footer dates.

An edited online reference published by National Institute of Standards and Technology. The authorship tags on individual chapters refer to the credited chapter contributors, not to authorship of the entire reference.

Official website: dlmf.nist.gov/

Project description: dlmf.nist.gov/about/

Chapter 2 contributors: Frank W. J. Olver, Roderick S. C. Wong. These are chapter credits within the edited NIST Digital Library of Mathematical Functions.^[ref]

Publisher: National Institute of Standards and Technology.

Online text: dlmf.nist.gov/2.11

Online reference release inspected: version 1.2.8, 15 September 2026. This date identifies the site release.

Cited passages: NIST Digital Library of Mathematical Functions, §2.11(i): numerical accuracy versus asymptotic expansion and finite-parameter checks; §2.11(iii): exponentially improved expansions.

Chapter 2 contributors: Frank W. J. Olver, Roderick S. C. Wong. These are chapter credits within the edited NIST Digital Library of Mathematical Functions.^[ref]

Publisher: National Institute of Standards and Technology.

Online text: dlmf.nist.gov/2.1

Online reference release inspected: version 1.2.8, 15 September 2026. This date identifies the site release.

Cited passages: NIST Digital Library of Mathematical Functions, §2.1(iii), equations 2.1.13–2.1.15: fixed-order inverse-power expansions and uniqueness; §2.1(v): generalized asymptotic scales and expansions.

Section of NIST Digital Library of Mathematical Functions. Chapter 3 author: Nico M. Temme, credited as N. M. Temme. National Institute of Standards and Technology issues and hosts the edited reference. The inspected online release is version 1.2.8, 15 September 2026; this is a site release date, not a section publication date. No separate subsection publication or revision date is established.

Online text: dlmf.nist.gov/3.5.ii

Chapter credit: dlmf.nist.gov/3

Full-name identity: dlmf.nist.gov/about/bio/NMTemme

Cited passages: NIST Digital Library of Mathematical Functions, §3.5(ii), equations 3.5.6–3.5.8.

Issued by National Institute of Standards and Technology.

Publisher: National Institute of Standards and Technology.

This source is credited to an organization.

Online text: www.nist.gov/programs-projects/pico-watt-acr

Cited passages: Description, Design Parameters for Improved ACR Sensitivity; Key Design Features: conical receiver, coating, constant-temperature loop and thin-walled Kapton link; Key Design Features, final paragraph: response time proportional to receiver heat capacity and inverse thermal conductance.

Page created 14 August 2015; updated 10 April 2025. These are web timestamps, not an independently verified initial apparatus-publication date.

By National Institute of Standards and Technology.

Official text: www.nist.gov/pml/nanoscale-device-characterization-division/popular-links/hall-effect/resistivity-and-hall

Institutional measurement procedures covering contact geometry, reversal of electric current and magnetic field, and extraction of sheet carrier density and Hall mobility. Bulk density requires the conducting thickness.