Which box system value can be the same as the A-measurement?

• A. A measurement
• B. B measurement
• C. DBL
• D. Effective diameter (ED)

Answer: (C)

In the box system for eyewear measurements, two different horizontal dimensions can sometimes line up: the width of a single lens (A measurement) and the distance between the two lenses (DBL, the bridge width). They can be numerically identical in frames where the bridge width happens to equal the width of one lens. In that case, the value shown for the distance between the lenses can match the A measurement exactly.

So, the reason this is the best answer is that DBL is the only box-system value among the options that can reasonably be equal to a single-lens width under certain frame geometries, whereas the B measurement is typically a vertical dimension, ED is the overall lens diameter, and A measurement itself is a single-lens width rather than a cross-lens distance.