A transfer standard apparatus for in situ calibration of measuring devices, the apparatus comprising: a manifold comprising: a first header in fluid communication with a second header via two or more flow lines (14, 16, 18), the first header and the second header each having ports (20, 320) at each end, the ports structured to enable external flow lines to be connected to the first header and the second header; two or more flow meters (340, 342), each having a flow capacity and disposed in one of the two or more flow lines such that the flow meters are connected in parallel relative to the first header and second header, wherein at least one of the flow meters has a lesser flow capacity than the other flow meters; and valves disposed in the flow lines adjacent the first header and the second header and operable to selectively isolate each flow meter from the first header and the second header; a mobile platform on which the manifold is mounted, the platform including access to the ports of the first header and second header; and a flow computer in communication with each flow meter and configured to receive signals from each flow meter and to determine a desired process value from measurement variables determined by each flow meter, wherein the apparatus further comprises a diverter flow line in fluid communication with at least two of the two or more flow lines and connected to each corresponding flow line by a multi-way valve at each end of the diverter flow line, the multi-way valve structured to selectively divert flow from one flow line to the other flow line via the diverter flow line such that the flow meters of the corresponding flow lines are fluidly connected in series. a manifold comprising: a first header in fluid communication with a second header via two or more flow lines (14, 16, 18), the first header and the second header each having ports (20, 320) at each end, the ports structured to enable external flow lines to be connected to the first header and the second header; two or more flow meters (340, 342), each having a flow capacity and disposed in one of the two or more flow lines such that the flow meters are connected in parallel relative to the first header and second header, wherein at least one of the flow meters has a lesser flow capacity than the other flow meters; and valves disposed in the flow lines adjacent the first header and the second header and operable to selectively isolate each flow meter from the first header and the second header; a first header in fluid communication with a second header via two or more flow lines (14, 16, 18), the first header and the second header each having ports (20, 320) at each end, the ports structured to enable external flow lines to be connected to the first header and the second header; two or more flow meters (340, 342), each having a flow capacity and disposed in one of the two or more flow lines such that the flow meters are connected in parallel relative to the first header and second header, wherein at least one of the flow meters has a lesser flow capacity than the other flow meters; and valves disposed in the flow lines adjacent the first header and the second header and operable to selectively isolate each flow meter from the first header and the second header; a mobile platform on which the manifold is mounted, the platform including access to the ports of the first header and second header; and a flow computer in communication with each flow meter and configured to receive signals from each flow meter and to determine a desired process value from measurement variables determined by each flow meter, wherein the apparatus further comprises a diverter flow line in fluid communication with at least two of the two or more flow lines and connected to each corresponding flow line by a multi-way valve at each end of the diverter flow line, the multi-way valve structured to selectively divert flow from one flow line to the other flow line via the diverter flow line such that the flow meters of the corresponding flow lines are fluidly connected in series.