The SI Base Units

Edition

The SI Brochure, The International System of Units (SI), 9th edition 2019, English PDF SI-Brochure-9-EN.pdf, V4.01 of June 2026 (https://doi.org/10.59161/AUEZ1291), pages 123 to 131. Kept: from Section 2.2, the statement “The International System of Units, the SI, is the system of units in which” with its seven items, the paragraph “where the hertz, joule, ...” and the sentence on the uncertainty of the constants; from Section 2.3.1, its first sentence, Table 2, the sentence that introduces the definitions, and for each of the seven base units its title, its definition (for the mole, its two paragraphs), the paragraph “This definition implies the exact relation...”, its equations, “which is equal to” where the brochure has a second equation, and the paragraph “The effect of this definition...”. Left out: the other paragraphs of those sections (previous definitions, realization, the Celsius temperature, the molar mass, Table 1, which repeats the seven constants) and the margin notes. The text was taken from the PDF with pdftotext and its superscripts and subscripts restored by script, checked against the pages: powers of ten and unit exponents are superscript, 133 before Cs is superscript, and the symbols are set in italic with their subscripts (the caesium frequency, N with subscript A, K with subscript cd, c, h, e, k, n, kT and the frequency nu), as the brochure prints them; the definitions are in bold, as printed. The brochure writes some minus signs of exponents with an en dash character (s–1, s–2, s–3 in the paragraph “where the hertz...”) and others with a minus sign: each is kept as it is. The increment sign (U+2206) of the caesium frequency, which no bundled font has, is set as the Greek capital delta (U+0394), which the printed page shows. The equations are set with KaTeX from the printed pages; the long ones, which the brochure sets on one line (on two for the candela), are broken before the “approximately equal” sign to fit the columns. The spaces between groups of digits and around the multiplication sign are set as no-break spaces. Table 2 is set as a table, its typical symbols in italic as printed. The header and the footer are written for the poster.

Rights

The SI Brochure is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Copyright statement of the SI Brochure, 9th edition, V4.01 (June 2026), on the page after its title page, https://www.bipm.org/en/publications/si-brochure. The footer credits the BIPM, names the brochure, its version and sections, links the license and says that the text is excerpted and the equations reset. The selection and layout are an original compilation under the MIT license of this repository.