Optional
ampereOptional
atmosphereOptional
barOptional
BritishOptional
calorieOptional
CalorieOptional
candelaOptional
Celsius_Optional
centimeterOptional
centipoiseOptional
centistokeOptional
dayOptional
decimeterOptional
Fahrenheight_Optional
footOptional
gallonOptional
gramOptional
hourOptional
inchOptional
JouleOptional
KelvinOptional
kilogramOptional
kilometerOptional
kiloOptional
kiloOptional
kiloOptional
literOptional
lumenOptional
meterOptional
micrometerOptional
micronOptional
mileOptional
milliampereOptional
millibarOptional
milligramOptional
milliliterOptional
millimeterOptional
millisecondOptional
minuteOptional
mmOptional
moleOptional
monthOptional
nanometerOptional
nanosecondOptional
NewtonOptional
ounceOptional
PascalOptional
poiseOptional
pound_Optional
pound_Optional
pounds_Optional
RankineOptional
secondOptional
shorttonOptional
slugOptional
stokeOptional
stoneOptional
tonneOptional
WattOptional
WattOptional
weekOptional
yardOptional
year
Is an object containing keys of units and values of nonzero exponents.