<P> When the user is unsure how a calculator will interpret an expression, it is a good idea to use parentheses so there is no ambiguity . </P> <P> Calculators that utilize reverse Polish notation (RPN), also known as postfix notation, use a stack to enter formulas without the need for parentheses . </P> <P> Some programming languages use precedence levels that conform to the order commonly used in mathematics, though others, such as APL, Smalltalk or Occam, have no operator precedence rules (in APL, evaluation is strictly right to left; in Smalltalk and Occam, it's strictly left to right). </P> <P> In addition, because many operators are not associative, the order within any single level is usually defined by grouping left to right so that 16 / 4 / 4 is interpreted as (16 / 4) / 4 = 1 rather than 16 / (4 / 4) = 16 . </P>

Who came up with the order of operations