Units and prefixes: Difference between revisions
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==Prefixes== | |||
y 10e-24 Yocto | y 10e-24 Yocto | ||
z 10e-21 Zepto | z 10e-21 Zepto | ||
| Line 25: | Line 25: | ||
Y 10e24 Yotta | Y 10e24 Yotta | ||
==Unit systems== | |||
===Unit systems, broadly=== | |||
<!-- | |||
Historic: English units [https://en.wikipedia.org/wiki/English_units] | |||
: based on a few things, including the on the Winchester Units for volume around the 1500s, and the Exchequer Standards (15something to 1825ish) | |||
: https://en.wikipedia.org/wiki/File:English_Length_Units_Graph.svg | |||
: leftovers from this era include foot, yard, acre, hectare, mile, pint, quart, gallon, ounce, pound, stone, and ton (though various not with the same meaning now) | |||
'''Imperial units''' [https://en.wikipedia.org/wiki/Imperial_units] | |||
: used in the UK since 1824ish | |||
: based on English units | |||
'''US Customary units''' [https://en.wikipedia.org/wiki/United_States_customary_units] | |||
: Based on English units | |||
Historic: centimetre–gram–second (CGS) | |||
: arguably a forerunner of metric/SI | |||
: there are various leftovers from cgs era still used one | |||
:: e.g. Oersted is a CGS unit, while in SI you'ld probably just write the Ampere per meter equivalent{{verify}} | |||
'''Metric''' / '''international units''' / '''SI''' | |||
SI is adopted by all countries except Liberia, Myanmar, and the United States. | |||
...but there are a few more footnotes to that than that. | |||
In particular, many countries that adopted SI habitually also still use older units they were used to. Some a few, some a bunch. | |||
: e.g. the UK uses some imperial units alongside metric, Canada ''more so''. | |||
: and many odder cases, often for historical reasons | |||
:: e.g. the Dutch have an ons and a pond, which are ''analogous'' to ounce and pound, but were never well standardized, and you might only still see it at places like the butcher's | |||
--> | |||
===Units that vary by location=== | |||
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Due to common origin US customary are similar enough that US customary also gets referred to to as imperial, and have units of the same name. | |||
Some of which have had different definitions over time, others still do. | |||
'''Things they agree on ''now'' ''' (seemingly often since when they decided to lessen the amount of confusion and mistakes, e.g. in trade): | |||
* '''yard''' (restandardized in 1834 and [https://en.wikipedia.org/wiki/International_yard_and_pound#History ye gods people, pick already]) | |||
* '''pound''' (at least since 1959's [https://en.wikipedia.org/wiki/International_yard_and_pound international yard and pound agreement]) | |||
* '''miles''' - ''mostly''. Most people saying 'mile' will mean the 1609.344 meter mile | |||
:: relatively few deal directly with the nautical mile (1852m thouth that too varied a few meters with time and place), used around boats, and planes, and space | |||
:: the US Survey Mile (and US statute mile usually refers to their survey mile), which is only slightly different at 1609.3472m and it only really matters in larger scale geography | |||
* '''inch''' - the inch we know today is exactly 25.4mm - but this has been only been agreed by Britain, America, and other countries (partly for industry reasons) since the 1930s | |||
: that said, they were already very close since the 1800s | |||
: before then it was vague, defined based on the size of typical barleycorn, with definitions like "three grains of barley, dry and round, placed end to end, lengthwise" which obviously varied more. | |||
'''Things they don't agree on to this day''' include: | |||
* '''ounce''' | |||
:: the British imperial fluid ounce is 28.413 ml, the US Customary fluid ounce is 29.573 ml | |||
:: which differs ~4% | |||
* '''pint''' | |||
:: the British imperial pint is 568.261 ml (20 of ''their'' fluid ounces), the US Customary pint is 473.176 ml (16 of ''their'' fluid ounces) | |||
:: which differs ~20% | |||
* '''quart''' | |||
:: the British imperial quart is 1.13 liters (40 UK of ''their'' fluid ounces), the US Customary quart is 0.94 L (32 of ''their'' fluid ounces) | |||
:: which differs ~20% | |||
* '''gallon''' | |||
:: the British imperial gallon is 4.54 liters (160 of ''their'' fluid ounces), the US Customary gallon is 3.78 liters (128 of ''their'' fluid ounces) | |||
:: which differs ~20% | |||
--> | |||
===Units that were always fairly local=== | |||
<!-- | |||
There are some units that are specific to a country, like | |||
* '''stone''' (UK) | |||
:: the UK stone as it is used today is 6.350kg (14 modern pounds), so people weigh order of 10 stone | |||
:: named for literal stones, but how heavy that was varied by what stone they picked as a reference, so varied by location - it used to be anything between 3kg to 15 kg | |||
:: https://en.wikipedia.org/wiki/Stone_(unit) | |||
* '''thou''', a.k.a. '''mil''' (milli-inch) | |||
: thousandths of an inch, which is 0.0254mm or 25.4 μm | |||
: which makes 1 millimeter very close to 39.37 thou | |||
: thou and mil are seen in non-metric countries, mostly around engineering, manufacturing. In particular around machining it is used as a unit in itself. | |||
: mil was once more common in the US, but now thou seems preferred to avoid confusion with millimeters | |||
--> | |||
==See also== | ==See also== | ||
* http://www.ex.ac.uk/cimt/dictunit/dictunit.htm | * http://www.ex.ac.uk/cimt/dictunit/dictunit.htm | ||
* http://www.lewrockwell.com/orig/kinsella6.html | * http://www.lewrockwell.com/orig/kinsella6.html | ||
Latest revision as of 16:47, 14 July 2023
Prefixes
y 10e-24 Yocto
z 10e-21 Zepto
a 10e-18 Ato
f 10e-15 Femto
p 10e-12 Pico
n 10e-9 Nano
u 10e-6 Micro
m 10e-3 Milli
(d) 10e-1 (0.1) Deci
(da) 10e1 (10) Deca
(h) 10e2 (100) Hecto
k 10e3 Kilo
M 10e6 Mega
G 10e9 Giga
T 10e12 Tera
P 10e15 Peta
E 10e18 Exa
Z 10e21 Zeta
Y 10e24 Yotta