HP 35s Scientific Calculator - Manual (Page 201)

Simple Programming 13-19
Stopping or Interrupting a Program
Programming a Stop or Pause (STOP, PSE)
Pressing  (run/stop) during program entry inserts a STOP instruction. This
will display the contents of the X-register and halt a running program until you
resume it by pressing
 from the keyboard. You can use STOP rather than
RTN in order to end a program without returning the program pointer to the
top of memory.
Pressing   during program entry inserts a PSE (pause) instruction.
This will suspend a running program and display the contents of the X–
register for about 1 second — with the following exception. If PSE
immediately follows a VIEW instruction or an equation that's displayed (flag
10 set), the variable or equation is displayed instead — and the display
remains after the 1–second pause.
Interrupting a Running Program
You can interrupt a running program at any time by pressing  or  . The
program completes its current instruction before stopping. Press  (run/stop) to
resume the program.
If you interrupt a program and then press  ,  , or   , you cannot
resume the program with  . Re-execute the program instead (  label line
number).
Error Stops
If an error occurs in the course of a running program, program execution halts and
an error message appears in the display. (There is a list of messages and conditions
in appendix F.)
To see the line in the program containing the error–causing instruction, press 
 . The program will have stopped at that point. (For instance, it might be a ÷
instruction, which caused an illegal division by zero.)