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”.
In the “Task Configuration” editor, on the Monitor tab, you can monitor the current value as well as the maximum and minimum values of the periodic jitter at runtime.
When the sum of all negative values Jper is not equal to the sum of all positive values Jper, a drift occurs.