optical lever(An experimental device used to measure angular rotation (e.g. in a galvanometer or torsion balance). Typically, a small mirror is attached to the rotating object, and a beam of light is directed onto the mirror and reflected onto a scale. The angle turned through by the beam is twice the angle turned through by the mirror.: Помимо оптиметра, принцип оптического рычага используется также и в оптических измерительных машинах.)
