Invariable
| Epoch | Confidence |
|---|---|
| 1 January 1 CE | Exact |
Overview
The Invariable calendar is a Gregorian-derived calendar proposed by L. A. Grosclaude in 1900 CE as well as by Gaston Armelin in 1887 CE. It features months in a repeating pattern of 30/30/31 days with New Years Day happening between December and January and Leap Day occurring between June and July in leap years, which happen in the same years as the Gregorian calendar. These two special days are not part of any week nor month, as if the calendar has paused for 24 hours.
The regular month lengths ensure that the first of every month always lands on a Monday, Wednesday, or Friday in a predictable pattern that is the same every year.
Info
| Calendar Unit | Days |
|---|---|
| New Years Day | 1 |
| January | 30 |
| February | 30 |
| March | 31 |
| April | 30 |
| May | 30 |
| June | 31 |
| (Leap Day) | 1 |
| July | 30 |
| August | 30 |
| September | 31 |
| October | 30 |
| November | 30 |
| December | 31 |
Accuracy
As this calendar is only a proposal, there really isn't anything to compare it to historically. It is intrinsically based on and locked to the Gregorian calendar, making it perfectly accurate.
Source
All of the information on this calendar came from its Wikipedia article.