EPHRAIM ISAAC cites the Ethiopic book of Enoch in an interview on the Ethiopic calendar:

Ethiopia: Scholar Says Ethiopian Calendar Neither Gregorian Nor Julian

The Ethiopian Herald (Addis Ababa)

December 29, 2006
Posted to the web December 29, 2006

ENA
Addis Ababa

A renowned Ethiopian born U.S scholar, Prof. Ephraim Isaac said that the Ethiopian calendar is unique in that it belongs neither to the Julian, nor to the Gregorian calendars.

He also said that close to 2,000 African-Americans living in the U.S have been organizing themselves to come to Ethiopia for the celebration of the New Ethiopian Millennium.
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Prof. Ephraim who is Director of the Institute of Semitic Studies in the United States, said that most scholars, including himself, believe Ethiopia has retained the old Egyptian system of calendar.

[...]

In addition to Mestehafe-Hissab, the professor said, there is a very famous book called, Mestehafe-henok, (The Book of Enoch) which is found only in Ethiopia with chapters that deals with some calculation of the years.

[...]

He's referring to the Astronomical Book, which was originally a separate and longer work, but now is found in chapters 72-82 of 1 Enoch. Extensive fragments of the original Aramaic Astronomical Book were found among the Dead Sea Scrolls.