For each modeling view (e.g. Calculation View) there is a history.
Accessible by right-click on the view -> "History"
This opens the History view (View of Eclipse - not a HANA view)
In the history view I can see the date and time of activation.
But how can I open an oder Version?
That history is the activation history - not a centrally retained history of all versions an object had during development.
However, in the Development perspective (not the Modeller perspective), there is a second History view available. This one allows comparison of different versions and checkout/rebase to an older version via right click menu.