This paper reports the coupling of HRTEM and moiré pattern observations, allowing the détermination of the thickness ratio of two superimposed crystals. Pseudo-lattice fringes are observed using identical TEM expérimental conditions as for observing moiré patterns. The pseudo-lattice spacing is first calculated in the dynamical theory Framework in two beam conditions. This approach shows a linear behavior of the spacing as a function of the thickness ratio of the two crystals. The rôles of sample crystallographic orientation and sample thickness on the thickness ratio détermination are discussed from multi-beam simulations. Finally, the method is applied on a bimetallic Cu Ag core-shell nanoparticle of a known structure. It is demonstrated that for this particle, the thickness ratio of Cu and Ag can be determined with an error that results in a précision less than 0.75nm on the Cu and Ag thicknesses. The advantages of the technique are the use of an in-plane sample configuration and a single HRTEM image