CALENDAR FRAMES · FIXED ERA STARTS

Fixed starts, two December 25 endpoints

Both 360-day era starts are fixed Julian dates in literal 6 BC.

Christ 360-era start

February 21, 6 BC · Julian

JD 1719282.5

Exodus 360-era start

March 23, 6 BC · Julian

JD 1719312.5

The fixed starts are 30 days apart

December 25, 1 BC

Julian endpoint · JD 1721416.5

Count fromElapsedOrdinal
Exodus era21042105
Christ era21342135

December 25, 1 BC

Gregorian endpoint · JD 1721418.5

Count fromElapsedOrdinal
Exodus era21062107
Christ era21362137

Two distinct instants, two days apart. These same-named December 25 dates are separate datums, not one date converted between calendars. Ordinal count = completed elapsed days + 1.

Figure 2. The two 360-day era starts remain fixed in the Julian calendar in 6 BC, 30 days apart. The Julian and Gregorian December 25 endpoints in literal 1 BC are separate instants, two days apart. Elapsed counts measure completed days; ordinal counts add the starting day.
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Fixed Julian era starts in 6 BC: Christ era February 21, JD 1719282.5; Exodus era March 23, JD 1719312.5, 30 days later. To Julian December 25 in 1 BC, the Exodus count is 2104 elapsed or 2105 ordinal, and the Christ count is 2134 elapsed or 2135 ordinal. To Gregorian December 25 in 1 BC, the Exodus count is 2106 elapsed or 2107 ordinal, and the Christ count is 2136 elapsed or 2137 ordinal. The two December 25 endpoints are physically two days apart.