An overview of scales in electrochemical systems and the interconnection between the different size regimes is presented. Within the context of experimental techniques for the investigation of ultrathin passive films, results on the Ti/TiO2 and Zr/ZrO2-systems are discussed. Electrochemical methods with high time and spatial resolution were employed to determine the dependence of optical, electrochemical and mechanical properties of the passive oxides on time, potential regime and crystal orientation. As electrochemical technology encompasses a sire regime of 12 orders of magnitude from technical applications in the km-and m-range to nanotechnology, it is vital to consider the causality of effects among different cell sizes. It is shown, that macroscopic processes such as long-term corrosion resistance can only be understood quantitatively if micro- and nanoscopic effects are considered and vice versa. The results point towards relationships between passivity and the spatial regime of experimental observation. As the sample size approaches the domain of the grain size of the metal substrate in the mu m-range, local heterogeneities are observed from grain to grain. With the example of passive Ti and Zr, it is shown that a quantitative understanding of corrosion and passivity requires investigations encompassing a wide range (m to nm) of size regimes.