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Since the exact definitions of many kinds of units have evolved over the
years, and since certain countries sometimes have local differences in
their definitions, it is a good idea to examine Calc's definition of a
unit before depending on its exact value. For example, there are three
different units for gallons, corresponding to the US (gal
),
Canadian (galC
), and British (galUK
) definitions. Also,
note that oz
is a standard ounce of mass, ozt
is a Troy
ounce, and ozfl
is a fluid ounce.
The temperature units corresponding to degrees Kelvin and Centigrade
(Celsius) are the same in this table, since most units commands treat
temperatures as being relative. The calc-convert-temperature
command has special rules for handling the different absolute magnitudes
of the various temperature scales.
The unit of volume "liters" can be referred to by either the lower-case
l
or the upper-case L
.
The unit A
stands for Amperes; the name Ang
is used
for Angstroms.
The unit pt
stands for pints; the name point
stands for
a typographical point, defined by `72 point = 1 in'. There is
also tpt
, which stands for a printer's point as defined by the
TeX typesetting system: `72.27 tpt = 1 in'.
The unit e
stands for the elementary (electron) unit of charge;
because algebra command could mistake this for the special constant
e, Calc provides the alternate unit name ech
which is
preferable to e
.
The name g
stands for one gram of mass; there is also gf
,
one gram of force. (Likewise for lb, pounds, and lbf.)
Meanwhile, one "g" of acceleration is denoted ga
.
The unit ton
is a U.S. ton of `2000 lb', and t
is
a metric ton of `1000 kg'.
The names s
(or sec
) and min
refer to units of
time; arcsec
and arcmin
are units of angle.
Some "units" are really physical constants; for example, c
represents the speed of light, and h
represents Planck's
constant. You can use these just like other units: converting
`.5 c' to `m/s' expresses one-half the speed of light in
meters per second. You can also use this merely as a handy reference;
the u g command gets the definition of one of these constants
in its normal terms, and u b expresses the definition in base
units.
Two units, pi
and fsc
(the fine structure constant,
approximately 1/137) are dimensionless. The units simplification
commands simply treat these names as equivalent to their corresponding
values. However you can, for example, use u c to convert a pure
number into multiples of the fine structure constant, or u b to
convert this back into a pure number. (When u c prompts for the
"old units," just enter a blank line to signify that the value
really is unitless.)
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