Basic operation: clicking "copy" button next to any TextField copies the
contents of that TextField to the "active" TextField indicated by the
selected radio button.  Selecting any item in the history choice element
will copy that element into the "active" TextField.  Answers to all
operations are displayed in "Register 3"

  This applet turned out to be more ambitious than I thought it was
going to be and thus, it barely works.  When you type a number into
the textfield, hit enter to register that number.  Next, click on the
desired operator.  Repeat this process and hit equals for you final
answer.  :)