Small calendar in Outlook view is gone

When sitting in the Calendar, and looking on the right hand side of the screen — one of my users has somehow turned off the small monthly calendar that is there.
They use the day view to see the scedule, and they also see the taskpad in the lower right hand side. But the monthly calendar that allows them to move to other days (and see them on the left) has gone away.
What can I do to get that back?