How do you measure love? All through history, it's been tried one way or another, from spells and amulets to trials to consultation with psychics. But as soon as we learned to harness electricity, machines to measure love, or more often sexual attraction, have sprung up everywhere. At the turn of the 20th century, a plethysmograph that detects chanes in volume was used to measure love. It's still used, but for other medical purposes. Medical instruments that measured temperature, heart rate, respiration, and blood pressure were combined to devise an early love meter, but also led to the lie detector. Other devices measure galvanic skin response or, as in the infamous Cupidometer, the subject's resistance to pain. The most enduring of the love-measuring instruments is the Love Tester, an arcade game that works on a completely different idea. Read about the history of love testers, both the serious and the entertaining, at Atlas Obscura.