def METHOD_NAME(self, spec=None):
    """ Return the size in the units indicated by the specifier.
        :param spec: a units specifier
        :type spec: a units specifier or :class:`Size`
        :returns: a numeric value in the units indicated by the specifier
        :rtype: Decimal
        :raises ValueError: if Size unit specifier is non-positive
        .. versionadded:: 1.6
           spec parameter may be Size as well as units specifier.
    """
    if isinstance(spec, Size):
        if spec == Size(0):
            raise ValueError("cannot convert to 0 size")
        return bytesize.Size.__truediv__(self, spec)
    spec = B if spec is None else spec
    return bytesize.Size.METHOD_NAME(self, spec)