11． What are datum features?

A: an actual feature (such as an edge, a surface, or a hole) on a part that is used to establish a datum and actually serves as a datum.

12. How are the measured elements represented on the drawing?

A: the measured elements are generally connected to the geometric tolerance frame through arrowed guide lines on the drawing, the datum elements are represented by datum symbols on the drawing. Note: datum feature ≠ datum.

13. What is a single element?

A: elements with shape tolerance requirements.

14. What are associated elements?

A: elements that have a functional relationship with other elements.

15. What is a functional relationship?

A: functional relationship refers to a certain certain direction and positional relationship between elements, such as vertical, parallel, coaxial, symmetrical, etc. That is, elements with positional tolerance requirements.

16. What are size factors?

A: a geometric shape determined by linear or angular dimensions of a certain size. Dimensional elements can be cylindrical, spherical, or two parallel corresponding surfaces, etc.

17．What are non-dimensional features?

A: there are no geometric shapes with large or small dimensions. Non-dimensional features can be surfaces and solid lines.

18. In straightness, what is the definition of the tolerance zone in a given plane?

A: the tolerance zone is the area between two parallel straight lines whose distance is the tolerance value t.

19．In straightness, what is the definition of the tolerance zone in a given direction?

A: when a direction is given, the tolerance zone is the area between two parallel planes whose distance is the tolerance value t. When two directions that are perpendicular to each other are given, the tolerance zone is the area where the normal cross-section size is the tolerance value t1×t2 area within the square prism.

20. In straightness, what is the definition of the tolerance zone in any direction?

A: the tolerance zone is the area within the cylindrical surface with a diameter of tolerance value t.