Precal is a lens calculation process which predetermines where
the thinnest part of a glazed lens will be, based on lens and
frame shape, prescription and centration. Precal calculates the
minimum centre thickness to which a lens can be surfaced to provide
the edge thickness specified by the dispenser. Futher
information about ordering is available in the lens catalogue,
product information
technical section.
PLUS FACTORS FOR
USING PRECAL:
Mid or high plus prescription
Plus cylinder axis of a toric lens running along the horizontal
± 30º (eg. +200/+250 x 165)
Varifocal lens
Lens with prism base up, down or out
Shallow eye shape
High decentration
PRECAL MAY ALSO BE USED:
To ensure the correct edging for rimless glazing, Supra glazing
and faceting
To balance thickness or weight of right or left lenses for both
minus and plus prescriptions
