
Unit Symbols



The IEEE/ASTM SI 101997 standard gives default symbols for a number of units that cannot be represented in an ASCII interface. For example, in Maple, the symbol for degree is deg, and the symbols for degrees Celsius and Fahrenheit are degC and degF, respectively. The angstrom has the abbreviation Ao.



Modifier Use for Plane Angles, Solid Angles, and Human Health Units



For plane and solid angles, radians and steradians are dimensionalized as modified ratios of lengths, namely length/length(radius) and length^2/length(radius)^2, respectively. For more information see the Units,angle and Units,solid_angle help pages.



Unit Display



In both the Standard and Natural environments, unless all units are associated with symbols or abbreviations, an expression is displayed using unit names. For example, joules per kilogram is displayed as $\frac{J}{\mathrm{kg}}$, whereas joules per clove is displayed as $\frac{\mathrm{joule}}{\mathrm{clove}}$. This does not conform to the IEEE/ASTM standards, in which the latter is written as the statement joules per clove.


Because there are limitations in Maple's prettyprinter, the symbol ohm($\mathrm{\Omega}$) (or any other Greek letter representing a unit symbol) is displayed as text when it has a prefix. For example, an ohm is displayed as $\mathrm{\Omega}$, but a milliohm is displayed as mOmega not $\mathrm{m\Ω}$.


In Maple output, there is no separation between groups of three digits. Furthermore, in documentation, the comma is used as a separator for groups of three digits when four or more digits appear on either side of the decimal marker. The IEEE standard is to use a space separator.



Unit Conversion Factors



In table A.1 of the IEEE/ASTM standard, the floatingpoint approximations for converting degrees, grad, and mil (angle) to radians, kilometers per hour to meters per second and lamberts to candela per square meter are labeled as exact conversions. In the Units package, the exact, rational conversion rates are used.


The unit kip is interpreted as 1000 Imperial pounds, whereas IEEE interprets it as 1000 Imperial poundforces. The latter is implemented as the unit kipf.


The table indicates that an acre equals 43560 square US survey feet, a chain equals 66 US survey feet, and a rod equals 16.5 US survey feet. Because these units are not intrinsically associated with US survey units, these conversions are used for US survey acres (acre[US_survey]), US survey chains (chain[US_survey]), and US survey rods (rod[US_survey]).


In all other cases, the Units package uses either the exact conversion rate from or a floatingpoint approximation at least as accurate as that listed in table A.1 of the IEEE/ASTM standards.



