Wow. I'm curious about this. [Not intended to be flamebait, just a comment on the issue]
I thought the default calendar is the Gregorian calendar, which a little wikipedia reading tells me it's one of the tropical solar calendars. The others listed are the Julian, Bahá'í, Hindu, Coptic, Iranian and the Thai solar calendar.
I don't even know if it is possible to change the default calendar in ZCS and, if so, how would one go about defining what this other calendar is given that there's a list one could choose from.
Solar calendar - Wikipedia, the free encyclopedia