There have been many different calendars in different societies, and there is much difficulty in converting between them, largely because of the impossibility of reconciling the irrational ratios of the daily, monthly, and yearly astronomical cycle lengths using integers.

[6] The authors design individual calendrical calculation algorithms for converting each of these calendars to and from a common format, the Rata Die system of days numbered from January 1 of the (fictional) Gregorian year 1.

[5] On the other hand, despite not being easy reading, reviewer Antonio F. Rañada recommends it not only to "mathematicians, astronomers or computer scientists, but also for historians or for any person interested in the cultural aspects of science".

Adding that the reduction of a human-produced calendar to a computer calculation is "sheer hubris", he nevertheless concludes that "We can be grateful that so useful a work of reference has been created from a project of such awe-inspiring futility".

[11] And reviewer Manfred Kudlek calls this "the most extensive and detailed publication on calendar systems" since the early 20th-century Handbuch der mathematischen und technischen Chronologie of Friedrich Karl Ginzel.