\label{Physical_Units}
\section*{Physical Units Accepted by LON-CAPA}
The following subsections show the physical units that LON-CAPA accepts. 
The symbols must be used when entering the units, for example {}``35 kg''.

Note that compound units are formed by using *, / and ^. For example, an acceleration might
be in terms of ``m/s^2'' or meters per second squared. This could also be expressed as``m/s/s''.
Units of Newton-meters (for torque) would be entered as ``N*m''. Parentheses may be used to guarantee
the correct sense of the unit. Kilometers per Ampere-hour could be written as ``km/(A*hr)'' or
``km/A/hr'' but not ``km/A*hr''. The last option would be interpreted as kilometer times hours per Ampere.

LON-CAPA will automatically perform some conversions between units of the same dimension
when units are provided for a problem.
You can provide an answer of ``1.45 km'' for a distance.
 If the computer expects the answer in cm, it will convert your answer before comparing
against the numerical solution.

Please note that if your units are inappropriate, the computer has no way of checking
the appropriateness of your answer.  If units are required, only once appropriate
units are provided will the system check your numerical answer.

\subsection*{Base Units}
\begin{verbatim}
# name      symbol     comment

meter           m      # length
kilogram        kg     # mass
second          s      # time
ampere          A      # electric current
kelvin          K      # thermodynamic temperature
mole            mol    # amount of substance
candela         cd     # luminous intensity
\end{verbatim}
\subsection*{Prefixes}
\begin{verbatim}
#   Prefix     symbol     factor

yotta            Y         10^{24}
zetta            Z         10^{21}
exa              E         10^{18}
peta             P         10^{15}
tera             T         10^{12}
giga             G         10^9
mega             M         10^6
kilo             k         10^3
hecto            h         10^2

deci             d         10^-1
centi            c         10^-2
milli            m         10^-3
micro            u         10^-6
nano             n         10^-9
pico             p         10^{-12}
femto            f         10^{-15}
atto             a         10^{-18}
zepto            z         10^{-21}
yocto            y         10^{-24}
\end{verbatim}
\subsection*{Derived Units}
\begin{verbatim}
# Derived Unit
# name       symbol    comment

gram            g      # mass
hour            hr     # time
minute          min    # time
day             day    # time
year            yr     # time
pound           lb     # mass
ounce           oz     # mass
inch            in     # length
foot            ft     # length
mile            mi     # length
yard            yd     # length
nautical_mile   n_mi   # length, nautical mile (UK)
rood            rood   # area, rood
acre            acre   # area, acre
hertz           Hz     # frequency
litre           L      # volume
newton          N      # force
pound_force     lbf    # force
dyne            dyn    # force
pascal          Pa     # pressure, stress
bar             bar    # pressure
mmHg            mmHg   # pressure, millimeter of mercury
torr            torr   # pressure
atm             atm    # standard atmosphere
joule           J      # energy, work, heat
electronvolt    eV     # energy
calorie         cal    # energy
Btu             Btu    # energy
watt            W      # power, radiant flux
coulomb         C      # electric charge
volt            V      # electric potential, electromotive force
ohm             ohm    # electric resistance, use this in /ANS
ohm             ohms   # electric resistance
ohm             Ohm    # electric resistance
ohm             Ohms   # electric resistance
siemens         S      # electric conductance
farad           F      # electric capacitance
tesla           T      # magnetic flux density
weber           Wb     # magnetic flux
henry           H      # inductance
radian          rad    # plane angle
degree          deg    # plane angle (Pi rad=180 deg)
steradian       sr     # solid angle
lumen           lm     # luminous flux
lux             lx     # illuminance
becquerel       Bq     # activity (radioactive)
gray            Gy     # absorbed dose (of radiation)
sievert         Sv     # dose equivalent (dose equivalent index)
astroUnit       AU     # mean distance earth to sun
celcius         degC   # multiplicatively OK
farenheight     degF   # multiplicatively OK
molarity        M      # chemisty
amu             amu    # atomic mass unit
amu             u      # atomic mass unit
\end{verbatim}
\subsection*{Interpretation}
The coded units are interpreted in the order of basic unit, 
derived unit, then prefix. For example, ``T'' will be matched against 
``tesla'' instead of considered the prefix ``T''. Another example is that 
``min'' will match
``minutes'' instead of treated  as a combination of the prefix ``m'' and units.