History from the side of those it happened to
Mathematics
| Year | Country | Category | title |
|---|---|---|---|
| 15 October 1582 | Italy | Mathematics | First day under the Gregorian calendar |
| 15 October 1582 | Italy | Mathematics | Leap-year arithmetic is revised |
| 15 October 1582 | Italy | Mathematics | Date conversion becomes a historical problem |
| 15 October 1582 | Italy | Mathematics | Calendar adoption reveals unequal political power |