Omar and I Skyped, and he shared the screen.
It turns out that the keyboard could not be used to make any entries in ncview.
The first suggestion was to restart the Mac, but Omar didn’t want to do that as a first thing to try, since he had lots of other windows open.
The second suggestion was to restart XQuartz (X windows). Omar tried this, and it solved the problem. The keyboard works with ncview running on his Mac, and he can change the range of the plots.
Patrick