Hi Roger,

In addition to the legend click method for doing this, you can hit
Alt-Z.

In theory, you could go into Settings... Toolbar, find a "Toggle
Zenith/North Up" option, and add a toolbar button for this function.
And you could set the hotkey associated with this function. For some
reason, though, this capability wasn't enabled... I've fixed this,
and in the next update, you'll be able to get the toolbar button
and selectable hotkey.

-- Bill