Did you know that Microsoft Excel can't do date calculations before January 1, 1900? True. Hasn't been updated since that's the way it was in the MS-DOS first release and original BASIC days. It doesn't do the logical thing and convert the negative values to absolute values and blah blah blah. It just gives you "##################" cells. Weird.
Anyway to deal with the past you have to shift your earliest date to after 01/01/1900 and shift all your other dates forward accordingly, which can introduce errors because 2000 did have a February 29 leap day but normally centuries do not. If you're striving for precision, you'll have to come up with a C++ program or something.
This came up because last week I had a hunch that turned out to be sort of true. The civil war was as long before World War II as we now are from World War II. Roughly.
Actually, August 4 of 2022 will be (+/- a day?) as long after the attack on Pearl Harbor as the attack on Pearl Harbor was after the firing on Fort Sumter.
Keep that date in mind as you go forward. It just might be the date of the beginning of Civil War 2.0 (if we last that long), or else perhaps the beginning or when we have to go save France again or something.
You heard it here first.