': Return the default unit for value, or None.
= INPUT VARIABLES
- value   The value or list of values that need units.
= RETURN VALUE
- Returns the default units to use for value.
Return the default unit for value, or None.'

@staticmethod
def default_units(value, axis):

    if (iterable(value) and (not isinstance(value, six.string_types))):
        return UnitDblConverter.default_units(value[0], axis)
    else:
        return UnitDblConverter.defaults[value.type()]
