'Convert the UnitDbl to a specific set of units.
= ERROR CONDITIONS
- If the input units are not in the allowed list, an error is thrown.
= INPUT VARIABLES
- units    The string name of the units to convert to.
= RETURN VALUE
- Returns the value of the UnitDbl in the requested units as a floating
point number.'

def convert(self, units):

    if (self._units == units):
        return self._value
    self.checkUnits(units)
    data = self.allowed[units]
    if (self._units != data[1]):
        msg = (u'Error    trying    to    convert    to    different    units.\n            Invalid    conversion    requested.\n            UnitDbl:    %s\n            Units:            %s\n' % (str(self), units))
        raise ValueError(msg)
    return (self._value / data[0])
