What connection is there between the Coptic calendar and the ancient Egyptian calendar?

The Copts inherited the ancient Egyptian calendar from their ancestors, and with some slight modifications, used it to order their liturgical Church life and their daily affairs, especially agriculture. The Coptic liturgical day begins at sunset, like that of the Jews and the Greeks; and each week consists of seven days, the first of which is the Lord’s Day (Sunday).

In the fourth century, many Copts were martyred, and they therefore considered the reign of Diocletian as a golden age. They set the year in which Diocletian became emperor (November, 284 A. D.) as the first year of their calendar. They introduced the term, “The Year of the Martyrs” ( Anno Martyrum ), abbreviated as A. M. The scholar Tertullian said, “If the martyrs throughout the world were to be put in one side of the scales and the Coptic martyrs alone were to be put in the other, the latter would outweigh the former.”⁶³⁷