The Working Group for Fluid Flow (WGFF) (a part of CIPM) has established the key comparisons for measurement of flow and volume covering volume, water, oil and gas flow measurement. This paper discusses the methodology of key comparison performed within flow and volume measurement and present the ultimate transfer standard package consisting of two different measuring principles. This opens the possibility to obtain Youden plots to distinguish between uncertainty contribution from the transfer standards and the facility. By putting the main part of the work in choosing and characterizing the transfer standards and minimizing the paper work, future Key Comparisons will benefit.