|horizontal centreline||line located at equal distance from the two horizontal tangents of the boxed lens (boxing) system (See 1 in Figure A.1.)|
|vertical centreline of box||line located at equal distance from the vertical sides of the rectangular box which circumscribes the spectacle lens shape (See 2 in Figure A.1.)|
|vertical symmetry axis||line located at equal distance from the nasal vertical sides of the rectangular boxes which circumscribe the right and left spectacle lens shapes (See 3 in Figure A.1.)|
|bridge width line||reference line for bridge measurements positioned 5mm below the horizontal centreline (See 4 in Figure A.1.)|
|bridge width *||minimum distance between the rims measured along the bridge width line (See e in Figure A.1.)|
|bridge height||distance from the bridge width line to the lower edge of the bridge, measured along the vertical symmetry axis (See f in Figure A.1.)|
|length to bend||length from the intersection of the dowel axis with the median plane of the joint to the intersection point of the axis of the tip and side, measured along the side axis (See l1 in Figure 2.)|
|length of drop||length from the intersection point of the axes of the side and tip to the end of the side (See l2 in Figure 2.)|
|effective diameter||diameter of the smallest circular uncut lens that can be glazed to the lens shape with its
geometrical centre positioned at the boxed centre (See Figure A.3.)
NOTE: This includes an allowance for edging.
|lens shape||outline of the lens periphery with the nasal side and the horizontal indicated|
|face form angle||angle between the plane of the spectacle frame and the plane of the right lens shape, or of the left lens shape (See Figure A.4.)|
|* For spectacle frames with adjustable pads, bridge width applies to the rims, not the pads; for rimless spectacles, it applies to the minimum distance between the nasal edges of the spectacle lenses measured along the bridge width line. (See Figure A.2.)
NOTE: Words in italics are terms defined with this International Standard.