By the time the Gregorian calendar was introduced in AD 1582, Illig alleges that the old Julian calendar should have produced a discrepancy of thirteen days between it and the real (or tropical) calendar.
Pada saat kalender Gregorian diperkenalkan tahun 1582 M, Illig menganggap kalender Julian lama "seharusnya" memiliki perbedaan tiga belas hari antara kalender tersebut dan yang asli (atau tropis).