Abstract A part definition drawing must accurately assume the functional require-
ments of the mechanical system to which it belongs to enable correct functional
dimensioning. This dimensioning is essential for the methods office to define its
production and for metrology to define its verification. It should be noted that the
functional dimensioning process we propose simulates a professional exercise in an
academic environment. In this paper, a method that uses a 3D model of a mechan-
ical system is adopted and the nominal models of the components. It also relies on
analyzing the positioning of each part in the possible working states of the mechanical
system. The part functional dimensioning requires mastery of the ISO-GPS language
(International Organization for Standardization-Geometrical product specifications),
and a precise analysis of the operation and positioning of each component. This anal-
ysis of the part positioning will allow the definition of the necessary datum systems
and the definition of the initial GPS specifications of dimension, tolerance zone
and pattern (maximum or least material requirement). Both analyses should provide
us with the ISO-GPS functional dimensions in the functional definition drawings
according to ISO 16792:2021 and other GPS standards.
