With real-time control, you can continually monitor and simulate a physical system. Real-time control applications repeatedly perform a user-defined task with a specified time interval separating them. Most real-time control systems monitor the physical system, compare the current state with the desired state, and then simulate the physical system based on the comparison. The time it takes to traverse this loop is considered the loop cycle time. This cycle time of the control loop varies based on the complexity of the system.

Determinism measures the consistency of the specified time interval between events. Many control algorithms, such as PID, require very deterministic behavior. For example, an elevator gradually moves to the correct floor because of the deterministic behavior of the control loop. Without the determinism, the elevator would still reach the correct floor but without stability.

With all real-time systems, there is some amount of error called jitter. Jitter is another way of measuring the determinism of a real-time system. You can calculate it as the maximum difference between any individual time delay and the desired time delay in a system, as shown in Figure 2 below.