The Calendar *should* be hanging somewhere in Chelsith when we first hear about it. After we raid Chelsith and kill the leviathan it is revealed that he was sitting on the Chelsith stone and it was given to us by Mayong Mistmoor for safe keeping...until he needs it. The rest of the calendar was excavated by Mayong's minions. We're not entirely sure if the calendar was left hanging in Chelsith or moved afterward. Also I seem to remember the hanging stones in Phara Dar's room were suppose to be a replica of the Shissar Calendar. The Monoliths are portions that plug into the calendar and probably contain a single planar rune each. How they work with the calendar isn't understood. Generally what we refer to as the calendar is actually only one of the 4 slabs, with the chelsith stone placed upon it.
