Final answer:
A stationary guideline for a blunt, zero-elevation haircut serves as a reference for maintaining a consistent length around the entire perimeter of the hair, ensuring precision and uniformity in the cut.
Step-by-step explanation:
The purpose of a guideline that doesn't move and is used for a blunt, zero-elevation haircut is to ensure consistency and precision throughout the haircut. This stationary guideline is essential because it serves as a reference point for the length of the cut for the entire perimeter of the hair. When performing a blunt or bob cut, where the hair should be of equal length all the way around the head with no layers, the guideline helps in achieving a clean and even edge with no elevation or layering.