Appendix A of the Calculator Tutorial says:
In order, to select cell which is a parent of a current cell, press Ctrl+Up. In order to select a child of a current cell, press Ctrl+Up.
I think that second one should be Ctrl+Down...
It occurred to me that the Calculator Tutorial would benefit from an introductory section (or link to such a section) that briefly describes development using MPS - i.e. how the idea for a DSL is realised using MPS, a generic overview and explanation of the sort of things that will be done in the tutorial.
The elements that make up an MPS project, how they interact and how they relate to the DSL.
Concepts - what they are, how they are used, how they contribute.
The various Editors - what part they play.
The Model - how it depends on the other elements.
Generators - how they fit in.
If I'd had a basic picture before starting the tutorial of what the pieces of the puzzle were, what they did, why they were needed, and how they fit together, I think I'd have had less trouble understanding it. The MPS editor is sufficiently different from the usual IDE editors that it takes a fair amount of mental effort just to mechanically follow the steps of the tutorial, without having to try and figure out how it all hangs together at the same time.