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Follow current literature
Use terminology and symbols commonly employed in the current literature for that subject and level of technicality. When in doubt, use the units of measure, prefixes, unit symbols, number notation, and methods of disambiguation most often employed in reliable periodicals directed to a similar readership.
The objective of technical writing is to communicate with minimal confusion so that readers can learn about a subject and are primed as well as possible to learn even more in their studies elsewhere. There are three important elements in determining what terminology and units of measure are best suited for a given article:
Preference for international units
- Wikipedia generally prefers international systems of measurement, such as the SI, over U.S. customary units or the imperial system. Unless there is a good reason to do otherwise, write "It was 1.83 meters (6 ft) tall", not the reverse.
- Wherever a discipline consistently uses its own units—either conventional or non-SI metric—this should be followed, since our readers should be able to converse with those knowledgeable in the discipline. For example:
- “a 450 cc Honda motorcycle engine” and never “a 450 ml” or “450 cm3 Honda motorcycle engine”;
- “Saudi Arabia exported 9.0 million barrels of crude”, but not “Saudi Arabia exported 1.43 million cubic meters of crude”;
- “a gravity gradient of 3.1 µGal/cm”, not “a gravity gradient of 3.1×10−6 s–2”, in the science of gravimetry.
- Parenthetical conversions should be given where appropriate and should generally also follow the practices in current literature on that subject unless there is good reason to do otherwise. Often the conversions will be to modern systems. To retain accuracy when quoting sources, editors should generally use the units used by your cited source as the primary value for that particular measurement. The selection of units for parenthetical conversion throughout an article is highly dependent on the subject matter. Even within the narrow discipline of piston engines in ground transportation, there is a range of permissible ways to show conversions; there is often no best way. For instance, writing "a 450 cc (450 cm3) motorcycle engine" is inappropriate even though it is in conformance with the SI; simply linking the first instance of “cc” to the Cubic centimeter article is sufficient. Writing "the Ford 351 Cleveland engine had an actual displacement of 351.9 cubic inches (5,766 cc)” is appropriate for a historical, American-made engine. And writing "the Dodge 5.7 L Hemi has a displacement of 5,654 cc (345.0 in3)" is appropriate for a modern, American-label engine that is classified in liters. But writing "the Ferrari Dino V12 engine has a displacement of 334.0 cubic inches" would be inappropriate in an article primarily about a European-made sports car.
- For some topics, there are multiple modern systems of measurement to choose from but some would generally be unsuitable for use in articles directed to a general-interest readership. For instance, the Planck units would typically be suitable only for advanced articles directed to expert readers—for example, an article on the mathematics of black hole evaporation—whereas an article on black holes directed to a general-interest readership should describe their mass in terms of solar mass. Level of difficulty also applies to the decision as to whether or not scientific notation should be employed in an article and, if so, at what magnitude it should begin. Here again, editors should look towards current literature on that subject for guidance in selecting level-appropriate units of measure, unit symbols, number notation, and terminology.