The pair write: "As people with symmetrical faces tend to be healthier and more attractive, they are also more self-sufficient and have less of an incentive to co-operate and seek help from others.

Single screw compressor cylinder by a screw and two symmetrical layout of the plane composed of stars round of meshing pair, installed in the chassis.

Imagine that these two couples are standing at either end of a pair of scales. They are evenly balanced, so this is a classic example of symmetrical balance.