The Phall-O-Meter is a satirical representation of the way that clinicians have historically determined whether visibly intersex children should be assigned female (and subjected to feminising surgeries) or assigned male (and subjected to masculinising surgeries). It was created by the Intersex Society of North America, based on research by Susan Kessler (1998):
In general, medical standards do not allow clitorises larger than .9 centimeters (about 3/8 of an inch). … [An image showing ranges of medically acceptable infant clitoral and penile lengths reveals] that intermediate area of phallic length than neither females nor males are permitted to have.
A copy held by the Wellcome Collection in London has been shared via Wikmedia Commons.