3.5
This is a fun little book of memory tricks. It really encompasses a wide-ranging number of topics. It isn't at its best as a "read all the way through it" book, but is great is small batches.
Teachers will appreciate the great ideas in here, and everyone is likely to know several of these.
The author has created some of them himself, with mixed success. I do like, however, that he encourages the reader (this is pitched at students in middle school or upper elementary, but is really good for high schoolers and adults, too!) to create them.
(Originally published as In 1492, Columbus Sailed the Ocean Blue)