Which measurement defines 3 cun?

The correct measurement that defines 3 cun is the distance from the middle of the eyebrows to the hairline. In acupuncture, a cun is a unit of measurement used to locate acupuncture points on the body, and it is based on specific anatomical landmarks.

The distance from the middle of the eyebrows to the hairline is often used as a foundational measurement because it is consistent across individuals and serves as an important reference point for locating other acupuncture points on the head and face. This reference is particularly useful for practitioners in clinical settings as it helps ensure accuracy in treatment.

Other options, while they may relate to measurements, do not specifically correspond to the cun measurement standard used in acupuncture practices. Understanding anatomical landmarks and their corresponding distances is crucial for practitioners when determining locations for acupuncture treatments, highlighting the importance of utilizing established measurement references.