In the boxing system, what does the B measurement represent?

The B measurement in the boxing system specifically refers to the lens depth, which is the vertical size of the lens when placed in a frame. It is crucial for determining how well the lenses fit within the selected frame and impacts how much of the lens area is utilized for vision, particularly important for multifocal lenses, such as bifocals or progressives. Understanding the B measurement is essential for ensuring that the lens height aligns with the wearer's visual needs, ultimately affecting their comfort and vision quality. This distinction is central to effective frame fitting and lens selection in optical practice.