We have the inspired, preserved word of God and he says you are not telling the truth...
After Gregory changed the calendar, the old Monday was still Monday. The old 7th day was still the 7th day.
Except that the old seventh day ended on our Sunday evening at 6 pm...
And what was the motive for changing it??? By changing it, it was impossible to keep any kind of accurate time since a mechanical or electrical means would be needed to know when one day ended and the next one started...
God had it worked out perfectly...When the sun went down you knew the day was over and the new one started...When the sun came up, you knew you were half way thru the (24 hour) day...
Wrong, the seventh day ends at sundown on Saturday for Jews, not Sunday.