Units

The xara.units submodule contains predefined constants that can help with keeping track of units.

Systems

The following systems are implemented (see Symbols below for definitions of the symbols):

	si	sim	us(f)	usi
Length	meter	mm	foot	inch
Force	N	N	lbf	lbf
Mass	kg	tonne	slug	lbf s2/inch
Stress	Pa	MPa	lbf/ft2	psi (lbf/inch2)
Energy	J (N × m)	mJ (10−3 J)	ft lbf	in lbf
Density	kg/m3	tonne/mm3	slug/ft3	lbf s2/in4

The idiom for importing constants from a system takes the form:

from xara.units.<system> import <symbols>...

where <system> is one of the implemented systems. For example, to import the symbols inch, kip, N and Pa from the us system,

from xara.units.us import inch, kip, N, Pa

Occasionally it is convenient to import all symbols using a star-import

from xara.units.us import *

Note, however, that this is generally considered bad programming style.

Symbols

Each submodule exports the following symbols:

Length

Symbols	Description
mm (also millimeter)	Milimeter
cm (also centimeter)	Centimeter
m (also meter)	Meter
km (also kilometer)	Kilometer
inch
ft (also foot)	International foot
yd (also yard)	International yard
mi (also mile)	Mile

Force

Symbols	Description
N (also newton )	Newton (force)
dyn (also dyne )	Dyne
pdl (also poundal)	Poundal
lbf (also poundf )
kip (also klbf )

Stress

Pa	pascal	Pascal, N/m:sup:2
torr
kPa	kilopascal	Kilopascal, 10:sup:3 Pa
MPa	megapascals	Megapascal, N/mm:sup:2 = 10:sup:6 Pa
bar
atm	atmosphere	Standard atmosphere
MPa	megapascal
GPa	gigapascal
psi		Pound-square-inch
ksi

Mass

slug
lbm	lbm	International avoirdupois pound
gm	gram
kg	kilogram	Kilogram
tonne		Metric tonne, 10 3 kg
oz	ounce	International avoirdupois ounce

Density

pcf

Pounds per cubic foot

Note

The p in pcf represents the pound mass (lbm), not the pound force (lbf) as it does psi unit.

Angular Velocity

rpm	revpm	Revolution per minute
radps		Radian per second