The Old World calendar was a calendar system used by Humans, but seemingly replaced by the Stardate system by the 23rd century.

Folsom points were found in the year 1925 of this calendar. (TOS: "The Galileo Seven")

In the script of "The Galileo Seven", this calendar system was instead called Old Earth calendar, and the year in which folsom points could be found was said to be 1926. An "Old Earth calendar" was implied to be in use in the 22nd century in "Up The Long Ladder".
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