# Frame geometry: A, B and bridge

In the boxing system, A is the horizontal width and B the vertical height of the box enclosing the lens shape. The bridge separates the two eyewire boxes.

## Reading a frame

Measurements should describe the shape being mounted. Nominal temple markings help identify the model but should be checked.

## Contour and orientation

Preserve units, scale, side and orientation when transferring a shape. A mirrored contour may look plausible on screen while being wrong for mounting.

## Limit

A and B do not describe the whole contour. Use the actual shape when the process depends on complete geometry.

## References

- [Laramy-K / OpticianWorks — ABO Study Guide](https://opticianworks.com/wp-content/uploads/2024/01/Laramy-K-OpticianWorks-Ultimate-ABO-Study-Guide-v6.23.pdf)

## Related topics

- [How to calculate horizontal decentration](https://lensas.com.br/en/knowledge/horizontal-decentration/)
- [Lens thickness: inputs needed for an estimate](https://lensas.com.br/en/knowledge/lens-thickness/)
- [Remote edging: what must travel with a shape](https://lensas.com.br/en/knowledge/remote-edging/)

Educational content · Fictional examples · Automated technical review, no claimed clinical validation.

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