A gas blending system , wherein said gas blending system provides blends of a first gas and a second gas in different mixing ratios, wherein the first gas is a standard gas with known concentrations of components and the second gas is a diluent gas, said gas blending system comprising (a) means for separately controlling the flow rate and/or pressure of a first gas stream supplied to each of two or more flow restrictor devices , arranged in parallel, wherein each flow restrictor device , has an inlet for receiving and an outlet for discharging a stream of the first gas, wherein said outlet is fluidly connected to means for measuring the pressure of the first gas stream discharged from the flow restrictor device, and wherein the dimensions of the flow restrictor devices , are different and selected such that each of said flow restrictor devices , produces a different controlled volumetric flow rate of the first gas stream at the outlet, and (b) means for controlling the flow rate of a second gas stream supplied to a multi-port flow selector device , wherein said multi-port flow selector device comprises an inlet (P1) for receiving and outlets (P2), (P6) for removing a stream of the second gas at a controlled volumetric flow rate, (c) a mixing zone respectively located downstream of each flow restrictor device respectively and the multi-port flow selector device , wherein each mixing zone respectively comprises a first inlet for receiving a stream of the first gas from the outlet of the flow restrictor device respectively fluidly connected to it, a second inlet for receiving a stream of the second gas from an outlet (P6) respectively (P2) of the multi-port flow selector device and an outlet for discharging a blend of the first gas and the second gas. (a) means for separately controlling the flow rate and/or pressure of a first gas stream supplied to each of two or more flow restrictor devices , arranged in parallel, wherein each flow restrictor device , has an inlet for receiving and an outlet for discharging a stream of the first gas, wherein said outlet is fluidly connected to means for measuring the pressure of the first gas stream discharged from the flow restrictor device, and wherein the dimensions of the flow restrictor devices , are different and selected such that each of said flow restrictor devices , produces a different controlled volumetric flow rate of the first gas stream at the outlet, and (b) means for controlling the flow rate of a second gas stream supplied to a multi-port flow selector device , wherein said multi-port flow selector device comprises an inlet (P1) for receiving and outlets (P2), (P6) for removing a stream of the second gas at a controlled volumetric flow rate, (c) a mixing zone respectively located downstream of each flow restrictor device respectively and the multi-port flow selector device , wherein each mixing zone respectively comprises a first inlet for receiving a stream of the first gas from the outlet of the flow restrictor device respectively fluidly connected to it, a second inlet for receiving a stream of the second gas from an outlet (P6) respectively (P2) of the multi-port flow selector device and an outlet for discharging a blend of the first gas and the second gas. <EOS>