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# System User's Guide: Operating System and Devices

## Converting Units of Measure (units Command)

You can convert quantities expressed in one measurement to their equivalents in another with the units command. The units command is an interactive command. It prompts you for the unit you want to convert from and the unit you want to convert to.

Note: This command only does multiplicative scale changes. That is, it can convert from one value to another only when the conversion involves a multiplication. For example, it cannot convert between degrees Fahrenheit and degrees Celsius because the value of 32 must be added or subtracted in the conversion.

The units command recognizes lb as a unit of mass, but considers pound to be the British pound sterling. Compound names are run together (such as lightyear). Prefix British units differing from their American counterparts with br (brgallon, for instance). The /usr/share/lib/unittab file contains a complete list of the units that the units command uses. You can also define new units in the unittab file or create and use your own File that overrides the standard conversion factor values in the unittab file.

Most familiar units, abbreviations, and metric prefixes are recognized by the units command, as well as the following:

 pi Ratio of circumference to diameter c Speed of light e Charge on an electron g Acceleration of gravity force Same as g mole Avogadro's number water Pressure head per unit height of water au Astronomical unit

For example, to display conversion factors for inches to centimeters, type:

```units

you have: in
you want: cm
```

Press Enter.

The units command returns the following values:

```* 2.540000e+00
/ 3.937008e-01
```

The output tells you to multiply the number of inches by 2.540000e+00 to get centimeters, and to multiply the number of centimeters by 3.937008e-01 to get inches.

These numbers are in standard exponential notation, so 3.937008e-01 means 3.937008 x 10-1, which is the same as 0.3937008.

Note: The second number is always the reciprocal of the first; for example, 2.54 equals 1/0.3937008.

For example, to convert a measurement to different units, type:

```units
you have: 5 years
you want: microsec
```

Press Enter.

The units command returns the following values:

```* 1.577846e+14
/ 6.337753e-15
```

The output shows that 5 years equals 1.577846 x 1014 microseconds, and that one microsecond equals 6.337753 x 10-15 years.

For example, to give fractions in measurements, type:

```units
you have: 1|3 mi
you want: km
```

Press Enter.

The units command returns the following values:

```* 5.364480e-01
/ 1.864114e+00
```

The | (vertical bar) indicates division, so 1|3 means one-third. This shows that one-third mile is the same as 0.536448 kilometers.

For example, to include exponents in measurements, type:

```units
you have: 1.2-5 gal
you want: floz
```

Press Enter.

The units command returns the following values:

```* 1.536000e-03
/ 6.510417e+02
```

The expression 1.2-5 gal is the equivalent of 1.2 x 10-5. Do not type an e before the exponent (that is, 1.2e-5 gal is not valid). This example shows that 1.2 x 10-5 (0.000012) gallons equal 1.536 x 10-3 (0.001536) fluid ounces.

If the units you specify after you have: and you want: are incompatible:

```you have: ft
you want: lb
```

The units command returns the following message and values:

```conformability
3.048000e-01 m
4.535924e-01 kg
```

The conformability message means the units you specified cannot be converted. Feet measure length, and pounds measure mass, so converting from one to the other does not make sense. Therefore, the units command displays the equivalent of each value in standard units.

In other words, this example shows that one foot equals 0.3048 meters and that one pound equals 0.4535924 kilograms.

See the units command in the AIX 5L Version 5.1 Commands Reference for the exact syntax.

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