24.1.1 Notation of unit objects
A unit object has two parts: a real number and a unit expression (a
single unit or a multiplicative combination of units). The two parts
are linked by the character _
(“underscore”). For example
2_m for 2 meters. For composite units, parenthesis must be
used, e.g. 1_(m*s).
See Table 24.1
for a list of the basic units.
| _A | Ampere | _ha | Hectare |
| _Angstrom | Angstrom | _hp | Horsepower |
| _Bq | Becquerel | _in | Inch |
| _Btu | Btu British thermal unit | _inH20 | Inches of water at 60° Fahrenheit |
| _Ci | Curie | _inHg | Inches of mercury at 0° Celsius |
| _F | Farad | _j | Day |
| _Fdy | Faraday | _kWh | Kilowatt-hour |
| _Gal | Gal (0.01 m/s2) | _kg | Kilogram |
| _Gy | Gray | _kip | Kilopound-force |
| _H | Henry | _km | Kilometre |
| _Hz | Hertz | _knot | nautical miles per hour |
| _J | Joule | _kph | Kilometers per hour |
| _K | Kelvin | _l | Liter |
| _Kcal | Kilocalorie | _lam | Lambert |
| _MHz | Megahertz | _lb | pound (16 oz) |
| _MW | Megawatt | _lbf | Pound-force |
| _MeV | Megaelectronvolt | _lbmol | Pound-mole |
| _N | Newton | _lbt | Troy pound |
| _Ohm | Ohm | _lep | Liter of oil equivalent |
| _P | Poise (measures viscosity) | _liqpt | US liquid pint (1 US gallon=8 US liquid pints) |
| _Pa | Pascal | _lm | Lumen |
| _R | Roentgen | _lx | Lux |
| _Rankine | Degree Rankine | _lyr | Light year |
| _S | Siemens | _m | Metre (unit) |
| _St | Stokes | _mho | Mho |
| _Sv | Sievert | _miUS | US statute mile |
| _T | Tesla | _mi^2 | Square international mile. |
| _V | Volt | _mil | Mil |
| _W | Watt | _mile | International mile |
| _Wb | Weber | _mille | Nautical mile |
| _Wh | Watt-hour | _ml | millilitre |
| _a | Are (100 m2) | _mm | Millimetre |
| _acre | Acre | _mmHg | Millimeter of mercury (torr), 0 degree Celsius |
| _arcmin | Minute of arc | _mn | Minute |
| _arcs | Second of arc | _mol | Mole |
| _atm | Atmosphere | _mph | Miles per hour |
| _au | Astronomical unit | _oz | Ounce |
| _b | Barn | _ozUK | UK fluid ounce |
| _bar | Bar | _ozfl | US fluid ounce |
| _bbl | Barrel | _ozt | Troy ounce |
| _bblep | Barrel of oil equivalent | _pc | Parsec |
| _bu | Bushel (8 UK gallons) | _pdl | Poundal (force) |
| _buUS | American bushel | _ph | Phot |
| _cal | Calorie | _pk | US peck |
| _cd | Candela | _psi | Pounds per square inch |
| _chain | Chain (66 feet or 22 yards) | _ptUK | UK pint (1 UK gallon=8 UK pints) |
| _cm | Centimetre | _qt | Quart |
| _ct | Carat | _rad | Radian |
| _cu | US cup | _rd | Rad (0.01 Gy) |
| _d | Day | _rem | Rem |
| _dB | Decibel | _rod | Rod 1 (5.029215842 m) |
| _deg | Degree (angle) | _rpm | Revolutions per minute |
| _degreeF | Degree Fahrenheit | _s | Second |
| _dyn | Dyne | _s | second |
| _eV | Electron volt | _sb | Stilb |
| _erg | Erg | _slug | Slug |
| _fath | Fathom | _sr | Steradian |
| _fbm | Board foot | _st | Stere |
| _fc | Footcandle (≈ 10.764 lux) | _t | Metric ton |
| _fermi | Fermi | _tbsp | Tablespoon |
| _flam | Footlambert | _tec | Tonne of coal equivalent |
| _fm | Fathom | _tep | Tonne of oil equivalent |
| _ft | International foot | _tex | tex (10−6 kg/m) |
| _ftUS | Survey foot | _therm | EEC therm |
| _g | Gram | _ton | Short ton (2000 pounds) |
| _ga | Standard freefall | _tonUK | Long (UK) ton |
| _galC | Canadian gallon | _torr | Torr (mmHg) |
| _galUK | UK gallon | _tr | tour (2π rad) |
| _galUS | US gallon | _tsp | Teaspoon |
| _gf | Gram-force | _u | Atomic mass unit |
| _gmol | Gram-mole | _yd | International yard |
| _gon | Grade | _yr | Year |
| _grad | Grade | _h | Hour |
| _grain | Grain (≈ 0,0648 grams) | _µ | Micron |
| Table 24.1: Physical units in Xcas |
If a prefix is put before the unit then the unit is multiplied by a
power of 10. For example, the prefix k or K, for
kilo, indicates multiplication by 103.
See Table 24.2 for a list of the unit prefixes.
| Prefix | Name | (*10^) n | Prefix | Name | (*10^) n |
| Y | yota | 24 | d | deci | −1 |
| Z | zeta | 21 | c | cent | −2 |
| E | exa | 18 | m | mili | −3 |
| P | peta | 15 | µ | micro | −6 |
| T | tera | 12 | n | nano | −9 |
| G | giga | 9 | p | pico | −12 |
| M | mega | 6 | f | femto | −15 |
| k or K | kilo | 3 | a | atto | −18 |
| h or H | hecto | 2 | z | zepto | −21 |
| D | deca | 1 | y | yocto | −24 |
| Table 24.2: Unit prefixes in Xcas |
You cannot use a prefix with a built-in unit if the result gives another
built-in unit.
For example,
1_a is one are, but 1_Pa is one pascal and not
10^15_a.
Examples
which is a unit object of value 10.5 meters.
which is a unit object of value 10.5 kilometers.