def to_si(self, values, from_unit):
        """Return values in SI and the units to which the values have been converted."""
        if from_unit == 'W/m2-K':
            return values, from_unit
        else:
            return self.to_unit(values, 'W/m2-K', from_unit), 'W/m2-K'
Return values in SI and the units to which the values have been converted.