Editing Carat (mass) (section)

==Historical definitions==
{| class="wikitable floatright"
|+ Carat before 1907<ref>{{cite journal
 |title=On the origin of the carat as the unit of weight for gemstones
 |first=Tao |last=Zhengzhang |journal=Chinese Journal of Geochemistry
 |date=July 1991 |volume=10 |number=3 |pages=288–293
 |doi=10.1007/BF02843332 |s2cid=127800966 |issn=1993-0364 }}</ref>
!style="text-align:left;"| Location !!style="text-align:left;"| mg
|-
| [[Cyprus]]		|| 187
|-
| ''unknown''		|| 188.6
|-
| [[Brazil]]		|| 192.2
|-
| [[Egypt]]		|| 195
|-
| [[Ambon Island|Ambonia]] || 197
|-
| [[Florence]]		|| 197.2
|-
| International carat<br>&nbsp; [[Jakarta|Batavia]], [[Borneo]], [[Leipzig]]
|style="vertical-align:top;"| 205
|-
| [[South Africa]] (1)	|| 205.304
|-
| London-New York (1)	|| 205.303
|-
| [[Spain]]		|| 205.393
|-
| London-New York (2)	|| 205.409
|-
| [[Berlin]]		|| 205.44
|-
| [[John Law's Company|Paris, East India]] || 205.5
|-
| [[South Africa]] (2)	|| 205.649
|-
| [[Amsterdam]]		|| 205.7
|-
| [[Lisbon]]		|| 205.75
|-
| [[Frankfurt]] (on Main) || 205.77
|-
| [[Vienna]]		|| 206.13
|-
| [[Venice]]		|| 207
|-
| [[Chennai|Madras]]	|| 207.353<!-- <br>207.36 -->
|-
| ''unknown''		|| 213
|-
| [[Bucharest]]		|| 215
|-
| [[Livorno]]		|| 215.99
|}

=== UK Board of Trade ===
In the [[United Kingdom]] the original '''[[Board of Trade]] carat''' was exactly {{frac|3|1647|9691}} [[Grain (unit)|grain]]s (~3.170&nbsp;grains = ~205&nbsp;mg);{{efn-lr|The pre-1888 [[Board of Trade]] carat, of which there were exactly {{frac|151|27|64}} per [[ounce#International troy ounce|ounce troy]], was approximately {{cvt|205.4094|mg}}.}} in 1888, the Board of Trade carat was changed to exactly {{frac|3|17|101}} grains (~3.168&nbsp;grains = ~205&nbsp;mg).{{efn-lr|The post-1887 Board of Trade carat, of which there were exactly {{frac|151|1|2}}; per ounce troy, was approximately {{cvt|205.3035|mg}}.}} Despite it being a non-metric unit, a number of metric countries have used this unit for its limited range of application.

The Board of Trade carat was divisible into four ''diamond grains'',{{efn-lr|Unlike the modern carat, the Board of Trade carat was not used for measuring pearls; those were measured with ''pearl grains''.}} but measurements were typically made in multiples of {{frac||1|64}} carat.

=== Refiners' carats ===
There were also two varieties of ''refiners' carats'' once used in the United Kingdom—the '''pound carat''' and the '''ounce carat'''.{{efn-lr|The refiners' carats were the offspring of the [[carat (purity)|carat as a measure of fineness for gold]].}} The [[pound (mass)#Troy pound|pound troy]] was divisible into 24 ''pound carats'' of 240 grains troy each; the pound carat was divisible into four ''pound grains'' of 60 grains troy each; and the pound grain was divisible into four ''pound quarters'' of 15 grains troy each. Likewise, the [[ounce#International troy ounce|ounce troy]] was divisible into 24 ''ounce carats'' of 20 grains troy each; the ounce carat was divisible into four ''ounce grains'' of 5 grains troy each; and the ounce grain was divisible into four ''ounce quarters'' of {{frac|1|1|4}} grains troy each.<ref>{{cite book| last= Chaffers| first= William|author-link=William Chaffers| year= 1883| title= Hall Marks on Gold and Silver Plate| edition= 6th| place= London| publisher= Bickers & Son}}</ref>

=== Greco-Roman ===
The ''solidus'' was also a [[Roman Empire|Roman]] weight unit. There is literary evidence that the weight of 72&nbsp;coins of the type called ''[[solidus (coin)|solidus]]'' was exactly 1 [[Roman pound]], and that the weight of 1&nbsp;''solidus'' was 24&nbsp;''[[siliqua]]e''. The weight of a Roman pound is generally believed to have been 327.45&nbsp;g or possibly up to 5&nbsp;g less. Therefore, the metric equivalent of 1 ''siliqua'' was approximately 189&nbsp;mg. The Greeks had a similar unit of the same value.<ref name="grierson">{{cite journal | last=Grierson | first=Philip | title=The Monetary Reforms of 'Abd Al-Malik | journal=Journal of the Economic and Social History of the Orient | volume=3 | year=1960 | pages=241–264 | doi = 10.1163/156852060X00098 | issue=3}}</ref>

Gold [[fineness]] in [[Fineness#Karat|carats]] comes from carats and grains of gold in a solidus of coin. The conversion rates 1&nbsp;solidus = 24&nbsp;carats, 1&nbsp;carat = 4&nbsp;grains still stand.<ref>{{cite journal |last1=Harper |first1=K |title=People, Plagues, and Prices in the Roman World: The Evidence from Egypt |url=https://www.cambridge.org/core/journals/journal-of-economic-history/article/people-plagues-and-prices-in-the-roman-world-the-evidence-from-egypt/50D27EAD5045D12C1573DFFB5D5C029C |journal=The Journal of Economic History |year=2016 |volume=76 |issue=3 |pages=803–839 |publisher=Cambridge University |doi=10.1017/S0022050716000826 |access-date=16 June 2019}}</ref> Woolhouse's ''Measures, Weights and Moneys of All Nations''<ref name=":0">{{cite book| last= Woolhouse| first= W. S. B. |title= Measures, Weights and Moneys of All Nations| url= https://archive.org/details/measuresweightsm00woolrich| year=1891}}</ref> gives gold fineness in carats of 4 grains, and [[silver]] in troy pounds<ref name=":0" /> of 12&nbsp;[[troy ounce]]s of 20&nbsp;[[pennyweight]] each.{{clarify|date=January 2012|reason=Why are we citing a 100+ year old book for information on current units, in a section on ancient units?}}