I'm not likely to ever use today's gem, but I am impressed. You can set NLS_CALENDAR in order to use other calendars, such as 'Arabic Hijrah'. Default, of course, is 'GREGORIAN'. I have no idea what other values are permissible. And I'm sure it's not possible for me to define my own calendar and use Shire dating, or my own custom calendar, or something. But still it's neat that they can handle that.