AFAIK compilers often/usually convert expression to postfix notation (RPN or close) during parsing. Also of course the Burroughs B5000 series and successors (up to B7800 IIRC) were stack machines, using postfix notation internally. At university a calculator was a necessity, I had an HP-25 and I always found that RPN made it a lot easier to keep track of where I was in complex calculations, e.g. when working out the reactance of some series-parallel-whatever network of R, L and C. The equations usually barely fitted on one line of a sheet of notepaper, involved lots of additions, subtractions, divisions and multiplications and conversions between rectangular and polar coordinates, and I did not envy those who used infix calculators. /Jonas