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I have a question on how to write units of measure of angles and times in my MSc thesis. What is the correct form between "13.2 degree" and "13.2 degrees"? A similar question about times: "32 day" or "32 days"? "1.2 year" or "1.2 years"? I have doubt because I read somewhere that in scientific documents (particularly in plots) it is better to not pluralize angles and units of time (about the latter statement, I read that is better to use (degree) instead of (deg) for units of measure in scientific plots).

Do you have a guide that illustrate rules about that?

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    I'm puzzled. Why would singular be "better"?
    – Buffy
    Dec 4, 2022 at 13:54
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    Yes, I think we would write 0.3 degrees and even 1.0 degrees.
    – GEdgar
    Dec 4, 2022 at 14:07
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    singular applies if there is 1 or less of the unit, so 0.3 degree and 1.3 degrees. The difficulty with English is hyphenation: “a 3-day wait to get a something”. Dec 4, 2022 at 14:09
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    @ZeroTheHero When you write quantities, don't use hyphenation. See here, §7.2. The reason is that the numerical value and the unit should be considered a single entity. Dec 4, 2022 at 14:14
  • @MassimoOrtolano This is an example from the section “ Hyphen in compound adjective with numbers” of Grammarly.com: “ The president of the company gave a 10-minute speech to the Board of Directors.” There is hyphenation when the compound word is used as an adjective. Dec 4, 2022 at 14:40

1 Answer 1

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The rules about writing quantities and units are described in the SI brochure.

In section 5.3, Unit names it is written (bold mine):

Unit names are normally printed in upright type and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title.

Therefore, when you write unit names in full, follow the rules for ordinary nouns, using the plural form as needed (e.g. 1.2 years).

Notice also, from section 5.3,

Although the values of quantities are normally expressed using symbols for numbers and symbols for units, if for some reason the unit name is more appropriate than the unit symbol, the unit name should be spelled out in full.

In plots, it's better to use unit symbols rather than names (see also this answer of mine on how to label axes in plots).

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