[pasc1878]

I would be careful on dates not just before 1582 but before 1753.

Great Britain and its colonies (which included USA) did not change to Gregorian until 1752 and also to confuse more changed the date on when the year changed from March to 1st January.

If you are in Greece or Russia be even more aware as that will be around 1920 when they changed.

[staplung]

You can see it on any unix system:

  $ cal sept 1752

     September 1752
  Su Mo Tu We Th Fr Sa
         1  2 14 15 16
  17 18 19 20 21 22 23
  24 25 26 27 28 29 30

[dreghgh]

This is frankly the cal developers being cute. Nothing requires this and the proleptic Gregorian calendar would have made more sense.

[KWxIUElW8Xt0tD9]

Britannica: "The Council of Nicaea in 325 decreed that Easter should be observed on the first Sunday following the first full moon after the spring equinox (March 21). Easter, therefore, can fall on any Sunday between March 22 and April 25."

The correct date for Easter was a huge deal in the early Church. The Pope brought Easter back into conformity with Nicaea by reforming the calendar -- astronomical knowledge had improved a lot over the centuries.

[madcaptenor]

Fortunately, Excel doesn't support dates before 1900.

[WillAdams]

For all the details on that see:

https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...

[pasc1878]

The article is not talking about Excel at that point.

But the program thw author is promoting says it does support dates before 1900.

I would worry what it does for dates between 1582 and 1753 in Anglo countries.

Basically you need to quote the date system as well as the date to get it correct. Even today there are countries not using Gregorian calendar.

I record dates as Julian days (or modified to not need a 32bit number) which is what Excel stores just using a different base date.

[madcaptenor]

OK, I see what you're referring to in the article. My bad.

[wruza]

No one really supports it or expects it to work. The best of what you can expect from an arbitrary date system is that it naively projects gregorian regime back into the past.

In precise-historian mode this makes sense, but otherwise people just don't care and count it as "gregorian days back".