Periodic jitter (Jper) is the deviation of the cycle time of a task (Tper) from the desired task cycle time (T0).
Jper = Tper - T0
The desired (ideal) cycle time T0 is specified in the configuration of the task as “Interval”.
You can monitor the current value, as well as the maximum and minimum value of the periodic jitter, on the “Watchdog” tab of the “Task Configuration”.
If the sum of all negative Jper values and the sum of all positive Jper values do not balance each other, then a drift results.