Orchidometer
![A schematic of an orchidometer](/Images/godic/202501/31/Orchidometr3343.png")
An orchidometer (or orchiometer) is a medical instrument used to measure the volume of the testicles.
The orchidometer was introduced in 1966 by Swiss pediatric endocrinologist Prof. Andrea Prader of the University of Zurich. It consists of a string of twelve numbered wooden or plastic beads of increasing size from about 1 to 25 millilitres. Doctors sometimes informally refer to them as "Prader's balls,", "the medical worry beads", or the "endocrine rosary."