Flow computers, totalizers, and rate indicators integrate the functions of flow and temperature measurement, computation, data acquisition, input / output (I/O) standardization, and closed loop control. They require external sensor inputs and may be used as local rate indicators. Some flow computers, flow totalizers and flow indicators are designed to monitor the flow of liquids. Others are used to monitor the flow of gases or mixed phases such as steam. Flow computers, totalizers and indicators that measure volumetric, velocity, and mass flow rates are commonly available. Volumetric flow rate indicates the amount of measured medium which flows past the sensor. Velocity flow rate is the speed of the medium. Mass flow rate represents the weight or mass of the medium and can be displayed in units such as pounds per minute (lbs/min).