Traditionally, tolerances are defined by a interval [min; max] which can lead to several ambiguous interpretations of conformity. In this paper, we will be examining an alternative method for setting specifications: "Inertial Tolerancing". Inertial Tolerancing consists in tolerancing the mean square deviation from the target rather than the distance. This alternative has numerous advantages over the traditional approach, particularly in the case of product assembly, mixed batches and conformity analysis. Coupled with a capability index Cpi, this alternative method reaches an interesting compromise between the quality of the assembled product and the cost of production. We propose to compare both approaches: traditional and inertial tolerancing.