Solomon Franco on the Zero Point for Trepidation

In the Middle Ages theories of trepidation, or accession and recession, were proposed to account for variable precession of the equinoxes; the values for trepidation were sometimes positive and sometimes negative, depending on the date. Several dates when the value
was 0º have been noted in the literature, and the Hebrew text of Solomon Franco (14th century) confirms two of them: about 18 years before the Hijra, and about 40 years before the Hijra.