Abstract When designing parts with tight tolerances, care must be paid to ensure that specified accuracy can be yielded despite manufacturing deviations. An issue to be considered is how deviations on datum elements propagate on toleranced features, taking into account configuration of locating fixtures used in manufacturing set-ups. The paper focuses on calculating position errors on machined features due to fixture configuration and tolerances on datums. Referring to some examples, it is shown how the most significant factors for tolerance control can be recognised by a proper geometric description of the locating fixture. The analysis is intended as a support to both fixture design and detection of critical aspects of part geometry and tolerancing scheme.