1. Introducing GD&T and GPS

The technical product documentation that is currently drawn up in many companies is unfortunately still ambiguous and contains many errors, such as erroneous datums, imprecise or missing distances, as well as incongruent and difficult to check tolerances. For about 150 years, a tolerancing approach called “coordinate tolerancing” was the predominant tolerancing system used on engineering drawings. This methodology in fact no longer results to be the most suitable for the requirements of the modern global productive realty, in which companies, for both strategic and market reasons, frequently resort to suppliers and producers located in different countries, and it is therefore necessary to make use of communication means in which the transfer of information is both univocal and rigorous. GD&T or GPS is a symbolic language that is used to specify the limits of imperfection that can be tolerated in order to guarantee a correct assembly, as well as the univocal and repeatable functionality and control of the parts that have to be produced.