Not all countries and civilisations use the same calendar system, although the majority of Westernized countries use the Gregorian calendar. It is now commonplace in 'none Gregorian' civilisations to use it alongside their own traditional system but can cause some confusion, in many African countries for example, the Gregorian calendar is used for most purposes but in some instances local traditional methods are still used, particularly when referring to Age, Length of marriage and ironically sentences for crimes. Most of these calendular calculations are based on a year that varies between 490 days and 512 days, which means that you can generally increase a persons age by at least 30% to get the 'Western Equivalent', and also explains the lengthy sentences handed out to criminals, and that brides appear to be very young, a practice that is more prevalent in the West of the continent. It is often taken for granted that they also use standard units of measurement, they do but again not that of the west, e.g. 12 stone of weight needs to have approx 1/3 added to it, and 8 " is the equivalent of a western 12"
