Unlike any other balance, this one makes it possible to physically show that –1<0. Weights placed on the outer pans represent negative integers and those placed on the inner pans represent positive integers. When you place a weight in each pan on one side of the centre post, the balance remains level as (–1)+(+1)=0. Great for small group work, the balance comes with four plastic pans, four plastic canisters, a set of plastic weights and a Teacher’s Booklet. Some assembly required.