'The unit attached to this parameter, if any.
On unbound parameters (i.e. parameters accessed through the
model class, rather than a model instance) this is the required/
default unit for the parameter.'

@property
def unit(self):

    if (self._model is None):
        return self._unit
    else:
        return self._model._param_metrics[self.name].get(u'orig_unit', self._unit)
