Guide
The first section cut to length, which every following section is matched against.
Also: guideline, guide length
A guide, or guideline, is the reference section a stylist cuts first. A stationary guide stays in one place and every section is brought back to it, which builds weight and length, as in a one-length bob. A travelling guide moves with the cut, each new section matching the one before, which is how even layers are made. Losing the guide is the most common cause of uneven cuts, so stylists check it as they work.