A system in which a fluid flows characterized by a change with time in space. A preselected place in the system is monitored to collect data at two or more time points correlated to a system event. The data is indicative of a system parameter that varies with time as a function of at least two variables related to system wash-in and wash-out behavior. To select time points a calibration map is calculated using color hue indicative of wash-out and color intensity indicative of wash-in. A color coded output map is developed. The calibration map, the color coded output map and image are novel implementations.