Mac Niocaill, The Irish medieval annals (Dublin 1975), 13. Easter tables were compiled to calculate the phases of the moon and the date for Easter Sunday. Mac Niocaill states that 'the earliest Irish annals appear to date from a couple of decades after the supersession at Iona of the Irish method of calculating Easter'. See also Dáibhí Ó Cróinín, 'Early Irish annals from Easter tables: a case restated,' in Peritia, 2 (1983), 74–86.