This button allows you to enter a new expression, or replace parts of an old one. To start off it is the only enabled button. When pressed a requester will appear allowing you to enter a new expression. Expressions are entered in fairly normal algebraic notation, but note * Multiplication is denoted by `*', division by `/', exponentiation by `^' * Multi letter variable names ARE allowed. Although they are entered all on one level they will be displayed as subscripts in the expression window. * The `*' for multiplication can be missed out when no confusion would arrise for example:- OK: 2a (a+b)(a-b) 2a(6c-3) NOT OK: 2ab means 2 times a_subscript_b 2a/b*c means ( 2 times a divided by b ) all times c * Brackets can be () or {}. The computer will automaticaly add/remove () brackets when appropriate. The computer will not remove {} brackets (exception - . * Functions are allowed, brackets are only needed where confusion could arrise. A function name must be followed by an open bracket or a space.