What we are demonstrating:

We begin the demonstration with an historical date: September 2, 1666. (Although the web program will allow you to choose your own.) This was the date that the Fire of London began and ravaged the city. Why this date? Interestingly enough, modern computers simply cannot calculate the day of the week correctly for this event. We actually have an article about this here

The issue is the fact that there was a calendar correction in England after 1666, which is totally ignored by modern computer operating systems. So, if you’re an historican, or dabbling in genealogy, you’ve probably learned not to trust any weekday information presented to you from modern computer programs.

We are a little more thorough. The conversion to the Gregorian Calendar was not something that happened overnight. Conversion largely depended upon which country you were in at the time.

England did not convert to the Gregorian calendar until 1752. On September 2, 1666, England was on the Julian calendar. Our web application here walks though the weekday of any day you specify for a large number of countries and their varying conversion dates to the Gregorian Calendar. To use: Select your date, hit calculate, and scroll down to see the results.

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If you were in the following locations:
Alaska, Alsace, American Colonies, Denmark, Egypt, England, Estonia, Faeroe Islands, Friesland, Greece, Iceland, Ireland, Latvia, Lithuania, Loraine, Netherlands, Norway, Protestant Germany, Romania, Russia, Scotland, Sweden, Utrech, Wales then you would have been on the Julian Calendar and the day of week for the day you selected will be:

If you were in the following locations:
Austria, Brixen, Carinthia, Czechoslavakia, France, Hungary, Italy, Luxembourg, Poland, Portugal, Prussia, Salzburg, Spain, Spanish Netherlands, Styria, Tyrol then you would have been on the Gregorian Calendar (the calendar we use today) and the day of week for the day you selected will be:

Here is a grid showing when the various countries adopted the Gregorian calendar, and how long that calendar has been in effect (from your selected day)