Cross-checking a haircut means:

Cross-checking means re-checking a completed haircut by parting and combing the hair in the opposite direction from how it was cut (for example, checking horizontal sections vertically) to verify that the lengths are even and the shape is balanced. It catches any unevenness that might be missed when viewing the cut only one way. Cross-checking is a mark of careful, professional finishing. Knowing this quality-control step and its purpose is part of the haircutting technique content on the exam.