In auxiliary constructions, the reference (fold) line must be perpendicular to the projection lines that carry features from one view to the next. Evaluate whether this rule is correct.

Introduction / Context:
The geometry of auxiliary views relies on orthogonality: projection lines must be perpendicular to the reference line to ensure accurate transfer of dimensions. The statement claims reference lines are always at right angles to the projection lines between views. We examine why this is standard practice.

Given Data / Assumptions:

• Reference line separates two corresponding views.
• Projection lines are drawn to carry points across views.
• Accuracy requires no directional scaling distortion.

Concept / Approach:
If projection lines are perpendicular to the reference line, distances measured along those projection lines transfer without skew. A non-perpendicular setup would introduce a directional cosine factor, distorting sizes and angles in the auxiliary view.

Step-by-Step Solution:
1) Draw the reference line to establish the rotation axis between views.2) Project all relevant points with lines perpendicular to that reference line.3) Transfer distances along or perpendicular to these projectors to place corresponding features.4) Join the transferred points to reconstruct edges and faces accurately.

Verification / Alternative check:
Constructing the same auxiliary with an oblique projector yields inconsistent lengths compared to known true sizes, revealing distortion.

Why Other Options Are Wrong:
Parallel requirement is false: parallel reference and projector lines give no crossing and make transfer impossible.“Angle is arbitrary”: Any non-orthogonal choice distorts distances.

Common Pitfalls:
Letting the triangle slip and losing the 90° relation; mixing guide lines from different reference lines.

Final Answer:
Correct