$base :
$step :
$units :
convert( $value, $from, $to)
count()
Return the total count of units in our class.
offsetExists( $offset)
Does a unit exist?
offsetGet( $offset)
Get a Unit
offsetSet( $offset, $value)
Add a unit to our units.
offsetUnset( $offset)
We don't allow unsetting units.
current()
key()
next()
rewind()
valid()
base()
Return the base item class.
units()