Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 126)

Scan Theory
Chapter 8
8-8
Here is an explanation of the rungs in Figure 8.2:
Rung 1 - The count increments its accumulated value each time this rung
is true.
Rung 2 - This rung enables the counter to increment on the next scan. If
we did not have this rung, the counter would always be true and it would
not increment. Remember: Counters increment only on false to
true transitions.
Rung 3 - The timer times in tenths of seconds when we are counting. This
value is displayed on the industrial terminal screen.
Rung 4 - The average scan time is displayed beneath store 2 and store 3
in milliseconds. Replace store 1 using Editing a Get Instruction in a
Completed Rung, chapter 12. Replace store 2 and store 3 instructions.
Refer to three-digit math in chapter 13.
Rung 5 - The counter overflow bit is re-setting the timer.
Rung 6 - The counter overflow bit is resetting the counter.