Ancients' Criterion of Earliest Visibility of the Lunar Crescent - how Good is it

Earliest visibility of the lunar crescent is an important calendrical element. It was needed in all early calendars and remains in use on some lunar calendars today. An astronomical criterion of earliest lunar visibility was therefore evolved quite early, using observations, right from the Babylonian era. Recently, an improved and comprehensive global criterion of earliest visibility, developed by the author, has been used to generate an extensive inverted moonset lag data set. These data, as a function of latitude and season, all for the first time provide a useful comparison with the simple ancient criterion.