- The ENTER key on a calculator is a clear sign that it employs the Reverse Polish notation or RPN
method to evaluate mathematical expressions. My first RPN calculator was the 1978 model HP32E
which I owned and used for over 20 years. My first serious programming was done on an HP41C
, basically a handheld computer which was also used as the third level backup system computer for the first nine space shuttle missions. It's always fun to hand your RPN calculator to an unsuspecting victim and watch them search for the nonexistent "=" key - its a geek thing. Canon 40D, 1/500 sec @ f/2.0, 50mm macro lens.
It's also got great space race aesthetics.