A method of and a device for accurately positioning a measuring means such as a measurement probe relative to that target area of a living body which has a unique marking peculiar to the living body. A transparent sheet member is first applied to the target part, and an image of the unique marking is then transferred onto the transparent sheet member. The transparent sheet member bearing the image of the unique marking is associated with the measuring device so that a subsequent measurement can be performed by the measuring device after the image transferred onto the transparent sheet member has been aligned with the unique marking in the target area.