Abstract: A system for automatically calibrating the accuracy of a flowmeter which is used for measuring the flow of fluid such as gas or liquid flowing therethrough. The system includes a calculator capable of performing mathematical functions responsive to receiving data signals and function command signals. A prover cylinder which includes a piston is provided for measuring the temperature, pressure, and time required for accumulating a predetermined volume of fluid. Along with these signals, signals representing the temperature and pressure of the fluid going into the meter are fed to a plurality of data registers. Under control of a process controller, which includes a program counter, a programmable read only memory, and decoder logic system, the data registers are read out and the information is fed through a data select circuit to the calculator. Command signals are also produced by a function select circuit and are fed to the calculator set indicating the desired function to be performed.