 Following up on Don Howard’s research, Kristian Camilleri (2006, 2007) points to the fact that complementarity was originally thought by Bohr (in his Como-paper) to exist between the space-time description and the causal description of the stationary states of atoms — and not between different experimental outcomes of the free electron. So the formulation of complementarity was restricted to the concept of stationary states because only there does the system have a well-defined energy state independent of any measurement. This observation deserves general recognition. But when Bohr rather soon thereafter began analysing the double slit experiment in his discussion with Einstein (1930), he had to extend his interpretation to cover the electron in interaction with the measuring apparatus.