# 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:

```\$ pint-convert 225lb
225 pound = 102.05828325 kg
```

use the –sys argument to change it:

```\$ pint-convert --sys US 102kg
102 kilogram = 224.871507429 lb
```

or specify directly the target units:

```\$ pint-convert 102kg lb
102 kilogram = 224.871507429 lb
```

The input quantity can contain expressions:

```\$ pint-convert 7ft+2in
7.166666666666667 foot = 2.1844 m
```

in some cases parentheses and quotes may be needed:

```\$ pint-convert "225lb/(7ft+2in)"
31.3953488372093 pound / foot = 46.7214261353 kg/m
```

If a number is omitted, 1 is assumed:

```\$ 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:

```\$ 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:

```\$ 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:

```\$ pint-convert 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 -p 20 Eh eV
1 hartree = 27.211386245988(52) eV

\$ pint-convert -p 20 -u 4 Eh eV
1 hartree = 27.21138624598847(5207) eV
```

The uncertainty can be disabled with -U):

```\$ pint-convert -p 20 -U Eh eV
1 hartree = 27.211386245988471444 eV
```

Correlations between experimental constants are also known, and taken into account. Use -C to disable it:

```\$ pint-convert --sys atomic m_p
1 proton_mass = 1836.15267344(11) m_e

\$ pint-convert --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.