Measuring · ABO
Progressive marking identifier
The ink layout has been cleaned off this progressive lens. Find the engravings, rebuild the prism reference point and fitting cross, read the add and measure the fitting height.
Preparing a lens…
Layout chart
Practice designs. The engraved circles are 34 mm apart, and the prism reference point is midway between them. Real lenses have their own chart; always check it.
| Nasal mark | Design | Fitting cross |
|---|---|---|
| ○ | Design Circle | 4 mm above the PRP |
| △ | Design Triangle | 2 mm above the PRP |
| ◇ | Design Diamond | 6 mm above the PRP |
The add is engraved under the temporal circle: “25” means +2.50 D. Fitting height runs from the fitting cross down to the lowest point of the lens.
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