The findings of an investigational study comparing a hand held tongue depressor pupil gauge with a printed millimeter scale sheet are the focus of this article. A historical perspective of the development of various millimeter measurement scales and devices is included as well as a brief overview of the anatomy and physiology of the oculomotor (III) cranial nerve. The results of the study provide support for the use of millimeter scales as an effective means of measurement of pupil size. Increased reliability with the use of a hand held tongue depressor pupil gauge is demonstrated. Implications for nursing practice are summarized.