I need to figure out how to create a temporary `Calendar` object (a copy of a "permanent" calendar that already exists) so that I can manipulate the copy: `tempCal.add(unit, value)`. I need to keep the original calendar object unchanged, so I really don't want to call `add(unit, value)` on it directly.

Since none of my attempts at creating a copy actually worked, my current ugly hack is to call `permanentCal.add(unit, value)`, display the desired results, then call `permanentCal.add (unit, -value)` — which just seems, uncool.