This reverse-Polish notation calculator by Kevin is a very simple calculator implementation. It has a stack of depth 4, just like an HP calculator, and has the standard 4 operations (+,-,*./). Output is limited by the use of scoreboards to one decimal point, but input and calculation are not so limited. Some day I'll set up a better display for the calculator using sprites, allowing higher precision.
30 May 2007. I added sin, cos, tan, and arctan buttons. The arctan button is limited to 1 degree precision in the downloaded version (the Squeak interpreter), but has full precision on the web (the Java interpreter).