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When using the Haochen CAD drawing software to create drawings, it is sometimes necessary to make use of the features related to geometric tolerances. However, many beginners do not fully understand what CAD geometric tolerance inclusion conditions and reference frames are. Below, we will provide a detailed explanation! CAD form and position tolerance inclusion conditions: Inclusion conditions are applied to geometric features of variable size. The second field for tolerances displays the tolerance value; the type of tolerance can be specified in the first field, depending on the control type – for example, by adding a diameter symbol before the tolerance value. The box following the tolerance value shows the inclusion condition; when setting a tolerance, an inclusion condition symbol can be added after the tolerance value. Inclusion condition symbols can be used as modifiers for geometric features and feature tolerance values whose size can vary. It is mainly applied to geometric features with variable sizes: the maximum inclusion condition (denoted by M, also known as MMC), which represents the maximum capacity for inclusion within the limit dimensions of a feature. In MMC, the holes have the minimum diameter, while the shafts have the maximum diameter. The minimum inclusion condition (denoted by L, also known as LMC) refers to the minimum enclosing capacity of a geometric feature within its limit dimensions. In the LMC, the holes have the maximum diameter, while the shafts have the minimum diameter. Not considering the feature size (denoted by S, also known as RFS) means that the geometric feature can be any size within the limit dimensions. CAD geometric tolerance datum reference frame: A datum is a theoretically precise geometric reference that allows for the measurement and verification of theoretically precise points, axes, or planes, and is used to establish the tolerance zones for features. The tolerance value in the feature control box can be followed by up to three optional datum reference letters and their modifiers. Generally, two or three mutually perpendicular planes work best. They are collectively referred to as the baseline reference frame. The reference frame used to verify part dimensions is shown in the figure below. The above covers the information regarding tolerance constraints and reference frames in the HaoChen CAD drawing software; it is hoped that those who are just starting to learn this software will be able to understand what CAD tolerance constraints and reference frames are after reading this article~