Datums and datum system definition according to GPS – Methodological principles

Datums and Datum Systems are basic concepts in the Geometrical Products Specification (GPS), which allow to define the position and the orientation of the tolerance zones. Aim of this work is to analyse the related ISO Standards and Drafts, firstly evidencing and comparing the main elements and basic principles. Focusing the attention on ISO Drafts, a deeper analysis aims at evaluating if the revision of the existing standards coherently refers to GPS principles, also considering examples of application of the described rules. A methodology collecting the main guidelines, which have to be considered when revising or developing GPS standards on Datums, is thus proposed. On the basis of the chain links concepts, some guidelines are defined, aiming at ensuring the rule of unambiguity, the rule of totality and the rule of complementarity, according to the GPS Masterplan. Moreover, it is underlined the need of maintaining a “high degree of applicability” of the standards, avoiding the risk of developing just an elegant collection of rules.