A device or assembly of devices designed for one or more of the following functions: to measure operating variables (such as pressure, temperature, rate of flow, and speed of rotation); to indicate these phenomena with visible or audible signals; to record them; to control them within a predetermined range; and to stop operations if the control fails. Simple instrumentation might consist of an indicating pressure gauge only. In a completely automatic system, desired ranges of pressure, temperature, and so on are predetermined and preset.