> And the transition from Julian to Gregorian just changed the leap year rules. It didn't change the fact that there's no year 0. It is not issue of Julian vs

> And the transition from Julian to Gregorian just changed the leap year rules. It didn't change the fact that there's no year 0. It is not issue of Julian vs Gregorian date, but the issue that ISO 8601 uses different conventions. Traditionally, there were two disjoint timelines (AD/CE and BC/BCE), both starting at year 1. Within these conventions, it make sense that first century is 1-100 CE, second century 101-200 CE and so on. ISO 8601 instead uses astronomical year numbering ( https://en.wikipedia.org/wiki/Astronomical_year_numbering https://en.wikipedia.org/wiki/Astronomical_year_numbering ), which has signed integer year numbers including year 0. Therefore, there is no beginning of timeline and most natural way how to define centuries by div 100, e.g. years 0-99 is century 0, and so on.