1.
2.
symmetrical in relation to the graduations,
aligned on the line corresponding to the PRP of the lens.
The PRP value of Essilor mid-distance lenses is 6 mm. This may vary depending on the manufacturer of the lenses.
To block the lens, refer to the section .Centering a lens > Blocking a lens (p.57)
b. Centering a lens using manufacturer markings
Prerequisite
The markings must be clear
The lens must at least have the following markings:
Centering cross
Centering marks
The lens is centered and ready to be blocked.>