Limiting diffusion currents, measured in electrodiffusion probes of friction, serve to detecting flow kinematics. Treatment of the primary current signal needs either direct calibration data from a viscometric cell or an information about probe geometry,depolarizer concentration and diffusivity. As a compromise, the auto-calibration (quantitative analysis of the voltage-step transient for a known electrode geometry) provides the concentration-diffusivity data for a given probe. The analysis is based on the Cottrell-Oldham asymptote of unsteady diffusion. A very-early stage of  the transient must be skipped in analysis because of secondary effects. The aim of the project is to improve the transient analysis by including the effects (i) of surface roughness, (ii) Ohmic loss, (iii) kinetics of electrode reaction. All these secondary effects of voltage-step transient were already studied in an uniformly accessible approximation. In the present stage, these effects will be studied in an adequate configuration using the Oldham's concept.