I too think RPN is much better than algebraic for many reasons, but many of my students do not. If I can convince them to spend the time necessary to get comfortable with RPN, they never turn back, but most would rather plug along with the familar if awkward notation they have learned over the years. It reminds me in many ways of student's resistance to learning how to solve systems of linear equations in any other than the first way they learned.
That brings me to the point I would like to make about Cabri, Sketchpad and RPN. Presumably, the software conventions will be new to the students, so they will learn whichever comes first. There is nothing intrinsically difficult about selecting the objects before the operation, so it should be just as easy to learn one as the other. I suspect the critical variable is which computer the students usually use. Mac and Windows students will probably be more comfortable with Sletchpad, since it emulates the MAC way of operating. Those who grew up with DOS will probably find Cabri easier at first. Either way, I don't think it is a big problem and certainly think it would be sort of silly to abandon the Sketchpad becuase HP abandoned RPN. (They really did not abandon it in the high level machines, only the 32)
Have a good day.
John Benson Evanston Township High School 715 South Boulevard Evanston Illinois 60204 Evanston IL 60202-2907 (708) 492-5848 (708) 492-5848