If you are interested in Calendars this book is a must have (but maybe not because you will already have the first edition). Most people seem to think that there is just one calendar. When pushed they remember that there are a couple of religious ones (Islamic and Jewish are the ones most remember).
This is a pity because marking the days as they pass (note that I did not write 'year') is a characteristic of human intelligence. However there is nothing special about chopping time into years, months and weeks. Days are pretty obvious if you live outside the Artic or Antarctic Circles. Years make sense if you live very far from the equator, but do the seasons even change in the Amazon Jungle? Noticing that we have a Moon makes a month a fairly obvious partition for time, but there is nothing special that says there should be seven days in something called a week.
Now if you want to find out about the various calendars that are still in use or about some of the more unusual ones that have been used in the past, this book is one to read.
This new edition includes a CD which now has the tools written in Java and Mathematica as well as the original Lisp versions.
This is an excellent mind-broadening book, though the less mathematical readers may have to skip some of the computational side. Even then the contents are interesting.