 Early manufacturing techniques fused a separate lens to the front surface, but modern processes cut all the geometry into a single piece of lens material.There are many locations, profiles, and sizes of add segments, typically referred to as segment type.Some "seg type" examples include Flat top, Kryptok, Orthogon, Tillyer Executive, and Ultex A. Trifocals contain two add segments to achieve a lens that corrects the person's vision for three distinct distances.