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The abbreviation for hundredweight
is "cwt" because "C" is the Roman symbol for 100. It is called
a hundredweight because it is 112 lb (well, it's close!). It
can also be called the long hundredweight to distinguish it
from what the Americans call the short hundredweight, which
is 100 lbs. So the long ton or UK ton is 2240 lbs, and
the short ton is 2000 lbs. The metric tonne is 1000 kg (about
2205 lbs). The word "ton" is derived from the same source as
that of a tunne of wine, a cask which held about 250 gallons.
Tons were in use in the late 1500's.
A dram is short for a drachm, but since
the avoirdupois drachm is different from the apothecaries drachm,
it could be that the name "dram" was used to help distinguish
it.
A pound is always written as "lb" to
prevent confusion with pound money "£". It is very old, traced
back to the Roman "libra" (which explains its abreviation!).
It was defined in England since Ethelred the Unready (968-1016).
In fact, a pound (money) was originally a pound (weight) of
silver, and the symbol for pound (money) £ is a stylized L.
The abbreviation for ounce is "oz". This comes from 15th century
Italian, also "oz" which is an abbreviation of "onza". "Oncia"
seems to be the modern Italian for ounce (although they use
metric measures now, of course) and I suppose that "onza" is
a variant of this. The word "ounce" comes from the Latin "unica"
or twelfth part. The ounce is a sixteenth part of a pound avoirdupois,
but it used to be a twelfth part of a pound troy. Troy weights
are now only used for precious stones and metals, but they used
to be the normal measure of weight. |
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Troy weight is a system
of weights used for precious stones and metals. The troy pound
is no longer in legal use, but gold is still sold in troy ounce
bars. Apothecaries weight was used for measuring drugs and medicines.
Both systems had the grain, ounce and pound in common (since
a troy ounce was the same as an apothecaries oz).
A pennyweight was called that because
it was the weight of a silver penny.
A scruple is derived from the Latin for
a small stone, because it's a very small weight. We also use
scruple to mean your conscience pricking you like a small sharp
stone in your shoe!
These weights were not learned at school,
because they had very specialized use. But our normal weights
tables were always marked as avoirdupois (which comes from Old
French "to have weight"). The troy system dates from the 10C.
The troy pound was defined as different from the avoirdupois
pound in the reign of Elizabeth I (1558-1603). See this Tudor
set of measures, where the table defines troy weights, and then
separates avoirdupois and troy weights without giving the conversion
factor! |
