I'm not being argumentative, just asking: what difference will this make with a calendar converter? I realize with an astronomy program it will make a difference, but surely software converting from one calendar to another would not change location between calendars?//
Oh, right. It shouldn't matter. But when comparisons were made with the calendar to some ancient Egyptian events they found good matches that were consistently a day off. I didn't look into this further beyond the suspicion that astronomers manipulated the timeline at one point, essentially eliminating a day from the calendar in connection with a manipulated astronomical picture. But that is far beyond my expertise. At one point I tried to get some professors in Hawaii to look at it, but ancient astronomy was just a class or two in their curriculum.Anyway, the unproven theory is, actually partly based on the VAT4956 vs. the Strm. Kambyses 400, that the Seleucids made some adjustments in the lunar times, only when they made the adjustments when discovered by modern astronomers, it made it seem the Earth's rotational speed was increasing. To distract from that picture, a day was gradually removed from the timeline, maybe just minutes at a time over thousands of years so that the references are a day off so that the Earth's rotational speed would seem to be slowing down, rather than increasing? In other words, a lunar position on one day might make it seem 12 hours early, but on the next day would seem 12 hours late. So they took a day out of the calendar to make it seem the Earth was slowing down rather than speeding up. And now with some ancient comparisons everything works only it's a day off, which would be a conversion issue. It's one of the jokes of ancient Greek astronomy. The revisionists ended making it seem the earth was moving slower back then than now, so that was fixed so that it seems the earth was moving faster back then than now, since it is more logical that the earth is slowing down due to lunar tidal drag or some other lame excuse then speeding up.
Now, there may be another reason you are getting a day off but that missing day has always been an otherwise unexplained mystery for really ancient comparisons, say from the Iron Age back for whatever astronomy they had. Eclipse times can be precisely corrected when you compare Ptolemy's canon and the Strm. Kambyses 400. When you do, observations are reflected a day earlier. With the current adjustments scientists have made with the so-called "delta-T", things are a day later, generally speaking.
Anyway, the converters don't work for really ancient dates. Apparently it is always a day off. An unproven suspicion is that modern astronomers have removed a day to support the deceleration theory, but that in reality, the Earth's rotational speed, using Egyptian records shows the Earth's speed has been constant as it is now, not varying even 1/100ths of a second.
So as others have suggested, in this field of imprecision, don't take it too seriously if you're getting some unexplained results. You have dishonest or incompetent translators on top of dishonest scholars on top of dishonest historians. At one point, you can only go so far. My routine was simply to calculate things two different ways, one based on the dating, one based on the actual astronomy, then compare the two.
Happy researching.