Once upon a time ""ten"" meant 10. And any 6th, 7th or 8th grade teacher attempting to suggest that ten could mean something else, or that it could be replaced by a base 8 or base 12 or base 2 system, would have been had up on charges of getting above himself, not to mention moral turpitude. But those dear days are dead. Tomorrow's nursery school diplomates will undoubtedly be whispering to each other in Boolean algebra to the distress of aging first grade teachers, who can only speak arithmetic. All this nonsense is in aid of introducing the Adlers' newest book. It teaches how to change Arabic numerals based on counting in groups of 10, to numbers based on counting in groups of 8, or 12, or 2, etc. Mr. and Mrs. Adler have done their usual inspired teaching here: their explanations of method and proof are clearly set forth with diagrams and charts. There are examples to work, with answers at the back of the book. The delicate innards of computers presently work on the base 2 system, and the final chapter illustrates this graphically. Accelerated math programs in the middle grades will find this valuable and students will find it easy to use on their own.