Some operations in VisIt may take a long time to complete so most computations are broken down into stages. In the event that you do not want to wait for an operation to complete, or if you realize that you made a mistake, you can interrupt a compute engine so it does not finish its work. When you click the Interrupt engine button a signal is sent to the compute engine that tells it to stop its work. The compute engine handles the interruption after it completes the current stage so there can be a small delay before the compute engine is interrupted. Any plots being generated when a compute engine is interrupted are sent into the error state and are listed in red in the Plot list until they are regenerated.