A method, comprising: providing a gas flowmeter installed to sense a flow of a gas in a pipe section of a gas pipeline, the gas flowmeter including an outer housing that includes an inlet , an outlet , a flow tube coupled to the outlet or the inlet, and at least one sensor positioned for sensing the gas flowing through the flow tube, a controller including an associated memory including a flow calibration algorithm and a flow measurement algorithm communicatively coupled to the sensor for receiving a sensing signal from the sensor, and for controlling operation of the sensor; wherein at least one of i) the gas flowmeter further comprises an integrated gas valve connected to the inlet or to the outlet, and ii) an additional external valve positioned outside the housing coupled to the inlet that provides at least two state operation; creating a zero-flow condition using at least one of closing or bypassing the integrated gas valve or manually closing the external valve; during the zero-flow condition measuring a measured gas flow; from the measured gas flow, determining a flow offset, and if the flow offset is determined to be outside a predetermined limit, in-line calibrating by adding the flow offset reflected as a correction factor to the flow measurement algorithm, characterized in that the integrated gas valve comprises at least one valve arrangement that provides an open position, a closed position where the gas flowmeter will not count the gas and a downstream installation will not receive the gas, and a bypass position where the gas flowmeter will not count the gas and the downstream installation will receive the gas, and wherein the determining of the flow offset is performable while the valve arrangement is in the closed position or in the bypass position. providing a gas flowmeter installed to sense a flow of a gas in a pipe section of a gas pipeline, the gas flowmeter including an outer housing that includes an inlet , an outlet , a flow tube coupled to the outlet or the inlet, and at least one sensor positioned for sensing the gas flowing through the flow tube, a controller including an associated memory including a flow calibration algorithm and a flow measurement algorithm communicatively coupled to the sensor for receiving a sensing signal from the sensor, and for controlling operation of the sensor; wherein at least one of i) the gas flowmeter further comprises an integrated gas valve connected to the inlet or to the outlet, and ii) an additional external valve positioned outside the housing coupled to the inlet that provides at least two state operation; creating a zero-flow condition using at least one of closing or bypassing the integrated gas valve or manually closing the external valve; during the zero-flow condition measuring a measured gas flow; from the measured gas flow, determining a flow offset, and if the flow offset is determined to be outside a predetermined limit, in-line calibrating by adding the flow offset reflected as a correction factor to the flow measurement algorithm, characterized in that the integrated gas valve comprises at least one valve arrangement that provides an open position, a closed position where the gas flowmeter will not count the gas and a downstream installation will not receive the gas, and a bypass position where the gas flowmeter will not count the gas and the downstream installation will receive the gas, and wherein the determining of the flow offset is performable while the valve arrangement is in the closed position or in the bypass position. <EOS>