AT&T 6300 Programmer's Manual page 54

Getting Started
2-36
If you enter a negative value for W, statement
40 is executed again, as statement 50 returns
control to statement Q for W) the system
displays an error message:
?Redo from start
and you must re-enter the value. This program
continues to run until you press CTRL
BREAK to stop execution. Your system
displays a "Break in nnnnn" message and
returns to Command Level. To resume
execution enter:
CONT