Answer:
sexual arousal
Step-by-step explanation:
A vaginal photometer is an instrument used in vaginal photoplethysmograph - a medical procedure that uses light to determine the amount of blood in the wall of the vagina. It is a procedure used to estimate or evaluate the level of sexual arousal in females.
A penile plethysmograph on the other hand is a device used to measure the blood flow to the penis during penile plethysmography procedure. It uses the same principle as the vaginal photometer and can be useful in the evaluation of erectile functions or sexual arousal in males.
Hence, both device measures sexual arousal in females and males respectively.