What tool is used to establish a guideline when cutting hair?

A comb is used to establish a guideline when cutting hair because it helps in sectioning and controlling the hair as it is being cut. When a stylist is creating a haircut, they typically part the hair into manageable sections. This allows them to see both the length they are cutting and to ensure precision in their technique.

By using a comb, the stylist can lift the hair away from the head to create the desired shape and length, making it easier to establish an even guideline. The guideline serves as a reference point for the rest of the haircut, helping to maintain uniformity and balance.

The other tools listed serve different purposes. Scissors are primarily used for cutting hair but do not establish guidelines on their own without the assistance of a comb. A razor can be utilized for texturizing or layering hair but is not typically used to establish guidelines. A brush, while helpful in styling and managing hair, lacks the precise control needed to establish a cutting guideline in the same way a comb does.