The Calendar
What the atlas records for this date, across the traditions it covers.
Observed On This Date
Falls on 31 March every year, the date chosen when the World Backup Day campaign began in 2011 after a Reddit post about losing a hard drive with no backup.
Dates for the Hebrew and Islamic calendars are the tabular reckoning, which is what a printed calendar prints. Communities that begin a month on a sighted crescent may differ by a day, and differ from one another by place.