Does the Standard define the Gregorian calendar?
Yes, ISO 8601 specifies how the Gregorian calendar works. The specification is completely compatible with the calendar specified by Pope Gregory XIII in 1582, except that ISO 8601 does not concern itself with the calculation of Easter. However, the calendar reference point used by the Standard is not Christ’s birth but the date on which the metric convention (“Convention du Metre”) was signed in Paris. The Standard defines that date to be 20 May 1875. Similarly, the reference point of the week cycles is 1 January 2000, which is defined to be a Saturday. Of course, these reference points are also completely compatible with common usage.
