1.3 definitionthe following terms a

1.3 definitionthe following terms are defined as their use applies in this standard.additionally，definitions throughout the standard of italicized terms are given in sections describing their application. their location may be identified by referring to the index.1.3.1 boundary，inner.A worst case boundary（that is，locus）generated by the smallest feature（MMC for an internal feature and LMC for an external feature）minus the stated geometric tolerance and any additional geometric tolerance（if applicable）from the feature’s departure from its specified material condition.see figs.2-9 through 2-121.3.2 boundary，outer.A worst case boundary（that is，locus）generated by the largest feature（LMC for an internal feature and MMC for an external feature）plus the geometric tolerance and any additional geometric tolerance（if applicable）from the feature’s departure from its specified material condition.see figs. 2-9 through 2-12.1.3.3 datum.A theoretically exact point，axis，or plane derived from the geometric counterpart of a specified datum feature. A datum is the origin from which the location or geometric characteristics of feature of a part are established.1.3.4 datum feature. An actual feature of part that is used to established a datum1.3.5 datum feature simulator. A surface of adequately precise form（such as a surface plate，a gage surface，or a mandrel）contacting the datum feature（s）and used to establish the simulated datum（s）.1.3.6 datum，simulated. a point，axis，or plane established by processing or inspection equipment，such as the following simulators：a surface plate，a gage surface，or a mandrel. See paras. 4.4.1 and 4.4.21.3.7 datum target. A specified point，line,or area on a part used to establish a datum.1.3.8 dimension.A numerical value expressed in a appropriate units of measure and used to define the size，location，geometric characteristic，or surface texture of a part or part feature.1.3.9 dimension,basic. A numerical value used to describe the theoretically exact size，profile，orientation，or location of a feature or datum target. See figs. 3-7. it is the basis from which permissible variation are established by tolerances on other dimensions, in notes, or in the feature control frames. See figs. 2-14, and 3-25.1.3.10 dimension，reference. A dimension，usually without tolerance，used for information purposes only. A reference dimension is a repeat of a dimension or is derived from other values shown on the drawing or on related drawings. It is considered auxiliary information and does not govern production or inspection operations. See figs. 1-17 and 1-18.1.3.11 envelope ,actual mating. This term is defined according to the type of feature，as follows:（a）for an external feature. A similar perfect feature counterpart of smallest size that can be circumscribed about the feature so that it just contacts the surface at the highest points. For example, a smallest cylinder of perfect form or two parallel planes of perfect form at minimum separation that just contact(s) the highest points of the surface（s）.For features controlled by orientation or positional tolerances，the actual mating envelope is orientated relative to the appropriate datum（s），for example，perpendicular to a primary datum plane.