To provide a method and a system for easily and surely monitoring with reproducibility, and adjusting if required, performance of one or more mass flow controllers (MFC) which supply manufacturing process with one or more gases.

The device, method and system for monitoring operation of one or more mass flow controllers which supply such processes as deposition, etching and others with gases are provided. This system is equipped with a bypass loop fluid spliced from either a process tube or a vent tube. In the bypass loop, a flow sensor like a digital mass flow controller is placed. The flow sensor detects one or more gas flow measurements from the mass flow controller, then the data from these one or more measurements are used to provide information on correctness and/or accuracy of the mass flow controller. Additionally, a method of correcting back pressure or negative vacuum in the process tube is also disclosed.