Abstract: Apparatus for determining the rate of hair growth by measuring the length of selected hairs at various times. An illuminated transparent member is provided with a recess adapted to receive the hair longitudinally, and to maintain it in an extended condition, and is graduated to visually display the length of the hair. The body area containing the hair to be measured is located by means of a mechanism having two arms, one of which arms is adapted to be placed against a reference point on the body while the other is adjustable to indicate the desired area.