 
 
 
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.
 
 
