You use the setting button at 8 o'clock. During normal use the LED at 12 blinks every minute. If you press the setting button and the seconds are between 1-30, the second hand stops and the LED blinks every second. If the seconds are 31-59, the second hand resets to zero and the LED continues blinking. The second hand will then start at the next press of the setting button.
this watch is in superb almost NOS condition with a few storage marks, needless to say it is running perfectly
note the red LED at 12.