I work as a freelance maths tutor. I have also taught maths in secondary schools and an FE college. I have worked in industry as a computer programmer / analyst. Calculators have their place but I believe in encouraging students to develop their skills in mental & paper arithmetic, and also using estimation as a means of checking the validity of numeric answers, as these are a solid foundation for higher mathematical topics. These also give students more confidence and understanding when facing exams. I also use IT tools like spreadsheets and GNU Graph, where appropriate, so that topics become more visual and interactive.