His learning was undoubtedly most extensive.

He quotes Eusebius, Orosius, Africanus, Bede, Josephus, Saint Jerome, and many other historical writers, and sometimes compares their statements on points in which they exhibit discrepancies, and afterwards endeavours to reconcile their conflicting testimony, and to correct the chronological errors of the writers by comparison with the dates given by others.

He also collates the Hebrew text with the Septuagint version of the Scriptures.

He uses the common era, though we have no reason to believe that this was done by the writers who immediately preceded him.

He also mentions the lunar cycle, and uses the dominical letter with the kalends of several years.[16] Another writer, _Gilla Caemhain_, was also contemporary with Flann and Tighernach.