PA0465 Console Scientific Calculator Program

                                                         
   Stack file operations are controlled from a window    
   entered by interrupting under 'Stack files' on line 3.
   The values in the answer stack can be stored into any 
   one of 20 files along with a user-entered title.      
   The values presently in the stack are unaffected by   
   the save. Restoring a file replaces the current stack 
   with the values from the file.