In GD&T, a datum is a fixed reference used to locate and orient features during measurement. The datum feature symbol marks the surface or feature that will serve as that reference. It identifies which physical surface establishes the datum, so the entire datum reference frame (the primary, secondary, and tertiary datums) is built from that surface or axis. This grounding lets tolerances like position or orientation be interpreted relative to a consistent origin in space. The symbol points to the actual surface used, not to manufacturing steps, material type, or finish.

The profile of a line defines the exact shape of the line’s boundary along its run, which determines the edge or contour you’re representing. It sets how the line curves or tapers along its length, not where the line is located relative to datums (that’s about position), not how long the line is (size), and not its orientation to a datum (orientation). So the profile controls the shape of the line used for edges or contours.

Composite tolerancing is used when you need to control the location of several related features with respect to more than one datum, using a single tolerance frame. For a well cap or plug, there are multiple features whose positions must stay coordinated to fit and seat correctly against a set of datums. Applying a composite tolerance lets you express all those relationships together, making both manufacturing and measurement more efficient because one tolerance frame governs how those features relate to the datum set rather than creating separate controls for each feature. Trying to limit just one feature at a time would require multiple separate tolerances and wouldn’t capture the needed interrelationship among the features and datums. Datums aren’t eliminated by a composite tolerance; they define the reference frame the part must relate to. And a composite tolerance isn’t about ignoring form—it governs location relative to datums, while form might be controlled by other, separate tolerances if needed.

The concept being tested is how much the angle of a rotating table is allowed to drift over time, specifically the maximum angular deviation permitted after a year. This annual angle tolerance reflects how stable the table's alignment is under normal use, including effects like wear, temperature changes, and calibration drift. A value of about 1° is a practical balance: it’s tight enough to keep measurements reasonably accurate over a year but not so strict that maintaining it would be prohibitively costly or frequent. If you set a smaller tolerance, like 0.5°, calibration and fabrication requirements become more demanding; if you allow a larger tolerance, such as 1.5° or 2°, the angular accuracy could degrade enough to affect precise measurements. In many standard specifications and QA practices, 1° is the commonly accepted annual limit, which is why that option is correct.