# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 1 Introduction  
Manufacturing metrology covers verification of whether produced parts fulfil functional requirements defined by a customer. A designer transforms functional requirements into dimensional and geometrical tolerances that limit actual part deviations and determine a part's performance [1, 2]. For example, roundness deviations and dimensional deviations of bearings and their adjacent components (shaft and housing) determine a cylindrical roller bearing's vibrational behaviour and fatigue life [3]. Assemblability of additive manufactured metal parts also depends largely on the size, flatness, cylindricity, perpendicularity and position tolerances of a part's geometrical features, along with their deviations [4]. The geometrical product specification and verification system developed in ISO by Technical Committee ISO/TC 213 (ISO GPS system) [5] is a set of concepts, principles, rules and symbols that enable description and clarification of how far geometrical features of an actual workpiece can be away from theoretically exact geometry (CAD model of a part) [6, 7, 8, 9, 10, 11]. The international standards that constitute the ISO GPS system are implemented as national standards in countries all over the world and are widely used in local and international companies. The foundation of geometrical specifications for the ISO GPS system are provided in ISO 1011 [12] and other International Standards give more detail [7, 8, 9, 10]. On the other hand, the US National Standard ASME Y14.5-2018 [13] also establishes uniform practices for stating and interpreting geometrical requirements. ASME Y14.5 is globally used because many USA companies locate their branches or look for suppliers in emerging countries that have lower labour costs. Both the ISO GPS system standards and ASME Y14.5 secure functional tolerancing and intend to provide uniformity in drawing specifications and interpretation. Some companies selected ASME Y14.5 muchbefore American companies started de-centralizing manufacturing from the USA to other countries, because nearly all of the info is in one document that is focused on design intent and there is the opinion that it is easier to understand [14]. Specification of functional requirements according to ASME Y14.5-2018 is quite often called geometric dimensioning and tolerancing, shortly referred to by the acronym GD&T. To improve the usability of ASME Y14.5-2018, the revised standard ASME Y14.5.1-2019 [15], which establishes the uniform mathematical basis for interpreting dimensional and geometrical tolerances, has been published. Nowadays, due to globalization, many suppliers face a challenge to work with two systems in parallel due to their customer requirements or supplier experience and capability. The ASME and ISO standards have many similarities in indications and definitions but in some aspects they are different. A careful comparison of ASME Y14.5 and the ISO GPS system tolerance indications enabled us to distinguish four cases:  
* Interpretation of the same symbols is always the same;
* Interpretation of the same symbols in certain cases is the same;
* Interpretation of the same symbols is never the same--the same symbols are intended to be used in different contexts;
* Some symbols (indications) are available only in one system. There are a few papers that have addressed the differences between the ISO GPS system and ASME Y14.5 [16,17]. In Appendix C to ASME Y14.5-2018, two tables are given to compare the symbols used in ASME Y14.5 with symbols available in the ISO GPS system. It is worth mentioning that in the opposite relation of comparison i.e., aiming to show how many symbols and modifiers defined in the ISO GPS system are available in ASME Y14.5-2018 standard, there would be a lot of comments not available in the ASME column. The tables given in ASME Y14.5-2018 indicate only if the same symbols are available in the ISO GPS system without any information as to whether the identical graphical symbol has the same meaning.