This is a great video by Worlds Last Chance. They explain this very well so I felt it was not worthwhile remaking, but rather point people to this video instead.
Many people just don’t see the difference between the calendars. They presume that all calendars have the same date line. But the scriptural calendar does not. It goes from one new moon to another new moon, which is not the same as the international date line.
This video shows the exact difference when one uses a fixed date line as opposed to when one uses the sun, moon and stars which He provided us.
N.B. Worlds Last Chance utilise the dark moon as the new moon, which is where this site differs, in that this site understands that there is Light upon this day in His word, and there is no light upon the fourth Sabbath.
We all have our eyes opened at different rates.