Units of measurement proliferate in science and engineering fields. Although you don’t need to check that the author is using the correct unit of measurement, you should recommend that they use one if it appears to be missing (e.g., “The reaction produced 9.52 of the chemical”: 9.52 what of the chemical?).
In addition, there are certain other unit-related issues that, as a proofreader, you should be aware of.
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The International System of Units (SI) defines the majority of unit names and symbols in use (although there are some common non-SI units). SI also makes recommendations regarding the typical quantity symbols in use.
Unit symbols are standardized across languages (for example, the Italian “chilometro” still uses the symbol “km”).
As such, it is not necessary to define any SI unit the first time it is used. In other words, it would be “The length of the field was 100 m,” not “The length of the field was 100 meters (m).”
When expressing the value of something in a scientific or technical text, the unit symbol is used rather than the name (so, 15 kg not 15 kilogram). In other texts, you should follow any style guide or the most appropriate use and aim for consistency.
The International Bureau of Weights and Measures (BIPM) sets the formatting and punctuation rules for SI unit names and symbols. It gives the following stipulations for SI units.
Unit symbols and accompanying numbers are written in upright (roman) type, regardless of the formatting of the surrounding text.
The grounds cover an area of 10 ha
Unit names follow the formatting of the text around them.
We measured the area covered by the grounds in hectares.
Recommended unit quantities are given in lower case and in italics. For example, time (t), mass (m), luminous intensity (Iv).
Unit symbols are given in lower-case letters unless they are derived from a proper name.
Kelvin: The triple point of water is 273.16 KMeters and seconds: The world record for the 100 m sprint is 9.58 s
Kelvin: The triple point of water is 273.16 K
Meters and seconds: The world record for the 100 m sprint is 9.58 s
There are two exceptions to this:
Either capital L or lower-case l is allowed for the liter, to avoid confusion between one (1) and the lower-case l.
The unit names for the symbols °C and °F are always given as degrees Celsius and degrees Fahrenheit, respectively.
Note that unit names (other than Celsius and Fahrenheit) are always given in lower case, even if derived from a proper name (1 watt = 1 W).
Unit symbols are seen as symbols, not abbreviations. Therefore, they do not need to be followed by a period unless they appear at the end of the sentence. They should never be interspersed with periods.
A half-high dot (·) is sometimes used to signal the multiplication of units. You don’t need to worry about inserting this, just don’t go deleting or commenting on it if it’s unfamiliar to you!
There should be a space between the number and the unit of measurement.
The device uses a 560 Ω resistor
Rules about whether to include a space before °C/°F vary. Most include one (CMoS does not).
There should be no space or hyphen between a prefix (e.g., centi- exa- tera-) and the unit name or symbol (e.g., it would be 1 µF or microfarad, not micro farad or micro-farad).
Here are some other useful guidelines for using SI units.
Although it’s not an SI unit, the percentage symbol (%) deserves an honourable mention here, as the rules are similar in some ways but not in others. Here’s some things to note.
When proofreading text that contains units of measurement, you should:
You do not (generally speaking) need to:
SI and non-SI units of measurement are found often in scientific and technical documents. As a proofreader, your responsibility is to ensure that spacing, capitalization, and punctuation are correct. You should also comment on any inconsistency or instances where units seem to be missing.
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