Book 2 provides the natural progression from Book 1. The first book left pupils wondering what would happen when they tried to add a tenth cube to a unit post that would only accept nine cubes. Book 2 teaches the concept that one 10 cube is the same as 10 units and by using the silver 10 number strip to exchange 10 units for one 10 cube placed on the silver post, they see for the first time the reason for the notation 1 and 0 meaning 10. This exchanging concept is further illustrated by the design of the ADDACUS^TM drawer which has a cash till connotation. Place value now makes more sense and the concepts such as subtraction by decomposition can be illustrated in a tactile way. Common mistakes are prevented by the fact that each 100's, 10's and units cube has a different core shape and therefore cannot be placed on the wrong post. Book 2 also teaches numbers 10 to 20 and then 20, 30, 40, to 100; multiplication and division, times tables. Addition, subtraction, multiplication and division of bigger numbers to 99 whilst only drilling number bonds of 10.