Pressure and volume flow control is a non-trivial problem in the range of minute molar fluxes. Requirements with regard to precision, stability and flexibility go beyond the specifications of commercially available systems. The present concept offers a functional solution for flexible dosage of norm volume flows down into the muL flow range providing at the same time a suitable pressure control. Furthermore an opportunity for in situ calibration of capillaries concerning their length and inner diameter is introduced. The described setup, after calibration, provides the possibility to determine the unknown viscosity of gaseous mixtures, which are very sparsely found in literature.