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.. _convert:
Command-line script
===================
The script `pint-convert` allows a quick conversion to a target system or
between arbitrary compatible units.
By default, `pint-convert` converts to SI units:
.. code-block:: console
$ pint-convert 225lb
225 pound = 102.05828325 kg
use the `--sys` argument to change it:
.. code-block:: console
$ pint-convert --sys US 102kg
102 kilogram = 224.871507429 lb
or specify directly the target units:
.. code-block:: console
$ pint-convert 102kg lb
102 kilogram = 224.871507429 lb
The input quantity can contain expressions:
.. code-block:: console
$ pint-convert 7ft+2in
7.166666666666667 foot = 2.1844 m
in some cases parentheses and quotes may be needed:
.. code-block:: console
$ pint-convert "225lb/(7ft+2in)"
31.3953488372093 pound / foot = 46.7214261353 kg/m
If a number is omitted, 1 is assumed:
.. code-block:: console
$ pint-convert km mi
1 kilometer = 0.621371192237 mi
The default precision is 12 significant figures, it can be changed with `-p`,
but note that the accuracy may be affected by floating-point errors:
.. code-block:: console
$ pint-convert -p 3 mi
1 mile = 1.61e+03 m
$ pint-convert -p 30 ly km
1 light_year = 9460730472580.80078125 km
Some contexts are automatically enabled, allowing conversion between not fully
compatible units:
.. code-block:: console
$ pint-convert 540nm
540 nanometer = 5.4e-07 m
$ pint-convert kcal/mol
$ 1.0 kilocalorie / mole = 4184 kg·m²/mol/s²
$ pint-convert 540nm kcal/mol
540 nanometer = 52.9471025594 kcal/mol
With the `uncertainties` package, the experimental uncertainty in the physical
constants is considered, and the result is given in compact notation, with the
uncertainty in the last figures in parentheses:
The uncertainty can be enabled with `-U` (by default it is not enabled):
.. code-block:: console
$ pint-convert -p 20 -U Eh eV
1 hartree = 27.211386245988(52) eV
.. code-block:: console
$ pint-convert -U Eh eV
1 hartree = 27.21138624599(5) eV
The precision is limited by both the maximum number of significant digits (`-p`)
and the maximum number of uncertainty digits (`-u`, 2 by default)::
$ pint-convert -U -p 20 Eh eV
1 hartree = 27.211386245988(52) eV
$ pint-convert -U -p 20 -u 4 Eh eV
1 hartree = 27.21138624598847(5207) eV
Correlations between experimental constants are also known, and taken into
account if uncertainties `-U` is enabled. Use `-C` to disable it:
.. code-block:: console
$ pint-convert --sys atomic m_p
1 proton_mass = 1836.15267344 m_e
$ pint-convert -U --sys atomic m_p
1 proton_mass = 1836.15267344(11) m_e
$ pint-convert -U --sys atomic -C m_p
1 proton_mass = 1836.15267344(79) m_e
Again, note that results may differ slightly, usually in the last figure, from
more authoritative sources, mainly due to floating-point errors.
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